[COMMITTED 2.31] Fix build with GCC 10 when long double = double.

[COMMITTED 2.31] Fix build with GCC 10 when long double = double.

[Szabolcs Nagy]

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backported this patch so we can build the 2.31 branch with
gcc-10 on arm-* targets.

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From de371d1581f379ada10163d9172a8fde676d13b4 Mon Sep 17 00:00:00 2001
From: Joseph Myers <joseph@codesourcery.com>
Date: Tue, 17 Mar 2020 22:57:42 +0000
Subject: [PATCH] Fix build with GCC 10 when long double = double.

On platforms where long double has the same ABI as double, glibc
defines long double functions as aliases for the corresponding double
functions.  The declarations of those functions in <math.h> are
disabled to avoid problems with aliases having incompatible types, but
GCC 10 now gives errors for incompatible types when the long double
function is known to GCC as a built-in function, not just when there
is an incompatible header declaration.

This patch fixes those errors by using appropriate
-fno-builtin-<function> options to compile the double functions.  The
list of CFLAGS-* settings is an appropriately adapted version of that
in sysdeps/ieee754/ldbl-opt/Makefile used there for building nldbl-*.c
files; in particular, the options are used even if GCC does not
currently have a built-in function of a given function, so that adding
such a built-in function in future will not break the glibc build.
Thus, various of the CFLAGS-* settings are only for future-proofing
and may not currently be needed (and it's possible some could be
irrelevant for other reasons).

Tested with build-many-glibcs.py for arm-linux-gnueabi (compilers and
glibcs builds), where it fixes the build that previously failed.

(cherry picked from commit 49348beafe9ba150c9bd48595b3f372299bddbb0)
---
 math/Makefile | 122 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 122 insertions(+)

diff --git a/math/Makefile b/math/Makefile
index 5985b6744b..3496af4040 100644
--- a/math/Makefile
+++ b/math/Makefile
@@ -644,6 +644,128 @@ ifneq ($(long-double-fcts),yes)
 # We won't compile the `long double' code at all.  Tell the `double' code
 # to define aliases for the `FUNCl' names.
 math-CPPFLAGS += -DNO_LONG_DOUBLE
+# GCC 10 diagnoses aliases with types conflicting with built-in
+# functions.
+CFLAGS-w_acos.c += -fno-builtin-acosl
+CFLAGS-w_acosh.c += -fno-builtin-acoshl
+CFLAGS-w_asin.c += -fno-builtin-asinl
+CFLAGS-s_asinh.c += -fno-builtin-asinhl
+CFLAGS-s_atan.c += -fno-builtin-atanl
+CFLAGS-w_atan2.c += -fno-builtin-atan2l
+CFLAGS-w_atanh.c += -fno-builtin-atanhl
+CFLAGS-s_cabs.c += -fno-builtin-cabsl
+CFLAGS-s_cacos.c += -fno-builtin-cacosl
+CFLAGS-s_cacosh.c += -fno-builtin-cacoshl
+CFLAGS-s_canonicalize.c += -fno-builtin-canonicalizel
+CFLAGS-s_carg.c += -fno-builtin-cargl
+CFLAGS-s_casin.c += -fno-builtin-casinl
+CFLAGS-s_casinh.c += -fno-builtin-casinhl
+CFLAGS-s_catan.c += -fno-builtin-catanl
+CFLAGS-s_catanh.c += -fno-builtin-catanhl
+CFLAGS-s_cbrt.c += -fno-builtin-cbrtl
+CFLAGS-s_ccos.c += -fno-builtin-ccosl
+CFLAGS-s_ccosh.c += -fno-builtin-ccoshl
+CFLAGS-s_ceil.c += -fno-builtin-ceill
+CFLAGS-s_cexp.c += -fno-builtin-cexpl
+CFLAGS-s_cimag.c += -fno-builtin-cimagl
+CFLAGS-s_clog.c += -fno-builtin-clogl
+CFLAGS-s_clog10.c += -fno-builtin-clog10l
+CFLAGS-s_conj.c += -fno-builtin-conjl
+CFLAGS-s_copysign.c += -fno-builtin-copysignl
+CFLAGS-s_cos.c += -fno-builtin-cosl
+CFLAGS-w_cosh.c += -fno-builtin-coshl
+CFLAGS-s_cpow.c += -fno-builtin-cpowl
+CFLAGS-s_cproj.c += -fno-builtin-cprojl
+CFLAGS-s_creal.c += -fno-builtin-creall
+CFLAGS-s_csin.c += -fno-builtin-csinl
+CFLAGS-s_csinh.c += -fno-builtin-csinhl
+CFLAGS-s_csqrt.c += -fno-builtin-csqrtl
+CFLAGS-s_ctan.c += -fno-builtin-ctanl
+CFLAGS-s_ctanh.c += -fno-builtin-ctanhl
+CFLAGS-s_dadd.c += -fno-builtin-daddl
+CFLAGS-s_ddiv.c += -fno-builtin-ddivl
+CFLAGS-s_dmul.c += -fno-builtin-dmull
+CFLAGS-s_dsub.c += -fno-builtin-dsubl
+CFLAGS-s_erf.c += -fno-builtin-erfl
+CFLAGS-s_erfc.c += -fno-builtin-erfcl
+CFLAGS-e_exp.c += -fno-builtin-expl
+CFLAGS-w_exp10.c += -fno-builtin-exp10l
+CFLAGS-e_exp2.c += -fno-builtin-exp2l
+CFLAGS-s_expm1.c += -fno-builtin-expm1l
+CFLAGS-s_fabs.c += -fno-builtin-fabsl
+CFLAGS-s_fadd.c += -fno-builtin-faddl
+CFLAGS-s_fdim.c += -fno-builtin-fdiml
+CFLAGS-s_fdiv.c += -fno-builtin-fdivl
+CFLAGS-s_finite.c += -fno-builtin-finitel
+CFLAGS-s_floor.c += -fno-builtin-floorl
+CFLAGS-s_fma.c += -fno-builtin-fmal
+CFLAGS-s_fmax.c += -fno-builtin-fmaxl
+CFLAGS-s_fmaxmag.c += -fno-builtin-fmaxmagl
+CFLAGS-s_fmin.c += -fno-builtin-fminl
+CFLAGS-s_fminmag.c += -fno-builtin-fminmagl
+CFLAGS-w_fmod.c += -fno-builtin-fmodl
+CFLAGS-s_fmul.c += -fno-builtin-fmull
+CFLAGS-s_frexp.c += -fno-builtin-frexpl
+CFLAGS-s_fromfp.c += -fno-builtin-fromfpl
+CFLAGS-s_fromfpx.c += -fno-builtin-fromfpxl
+CFLAGS-s_fsub.c += -fno-builtin-fsubl
+CFLAGS-s_gamma.c += -fno-builtin-gammal
+CFLAGS-s_getpayload.c += -fno-builtin-getpayloadl
+CFLAGS-w_hypot.c += -fno-builtin-hypotl
+CFLAGS-w_ilogb.c += -fno-builtin-ilogbl
+CFLAGS-s_isinf.c += -fno-builtin-isinfl
+CFLAGS-s_isnan.c += -fno-builtin-isnanl
+CFLAGS-w_j0.c += -fno-builtin-j0l
+CFLAGS-w_j1.c += -fno-builtin-j1l
+CFLAGS-w_jn.c += -fno-builtin-jnl
+CFLAGS-s_ldexp.c += -fno-builtin-ldexpl
+CFLAGS-w_lgamma.c += -fno-builtin-lgammal
+CFLAGS-w_lgamma_r.c += -fno-builtin-lgammal_r
+CFLAGS-w_llogb.c += -fno-builtin-llogbl
+CFLAGS-s_llrint.c += -fno-builtin-llrintl
+CFLAGS-s_llround.c += -fno-builtin-llroundl
+CFLAGS-e_log.c += -fno-builtin-logl
+CFLAGS-w_log10.c += -fno-builtin-log10l
+CFLAGS-w_log1p.c += -fno-builtin-log1pl
+CFLAGS-e_log2.c += -fno-builtin-log2l
+CFLAGS-s_logb.c += -fno-builtin-logbl
+CFLAGS-s_lrint.c += -fno-builtin-lrintl
+CFLAGS-s_lround.c += -fno-builtin-lroundl
+CFLAGS-s_modf.c += -fno-builtin-modfl
+CFLAGS-s_nan.c += -fno-builtin-nanl
+CFLAGS-s_nearbyint.c += -fno-builtin-nearbyintl
+CFLAGS-s_nextafter.c += -fno-builtin-nextafterl
+CFLAGS-s_nextdown.c += -fno-builtin-nextdownl
+CFLAGS-s_nexttoward.c += -fno-builtin-nexttoward -fno-builtin-nexttowardl
+CFLAGS-s_nexttowardf.c += -fno-builtin-nexttowardf
+CFLAGS-s_nextup.c += -fno-builtin-nextupl
+CFLAGS-e_pow.c += -fno-builtin-powl
+CFLAGS-w_remainder.c += -fno-builtin-remainderl -fno-builtin-dreml
+CFLAGS-s_remquo.c += -fno-builtin-remquol
+CFLAGS-s_rint.c += -fno-builtin-rintl
+CFLAGS-s_round.c += -fno-builtin-roundl
+CFLAGS-s_roundeven.c += -fno-builtin-roundevenl
+CFLAGS-w_scalb.c += -fno-builtin-scalbl
+CFLAGS-w_scalbln.c += -fno-builtin-scalblnl
+CFLAGS-s_scalbn.c += -fno-builtin-scalbnl
+CFLAGS-s_setpayload.c += -fno-builtin-setpayloadl
+CFLAGS-s_setpayloadsig.c += -fno-builtin-setpayloadsigl
+CFLAGS-s_significand.c += -fno-builtin-significandl
+CFLAGS-s_sin.c += -fno-builtin-sinl
+CFLAGS-s_sincos.c += -fno-builtin-sincosl
+CFLAGS-w_sinh.c += -fno-builtin-sinhl
+CFLAGS-w_sqrt.c += -fno-builtin-sqrtl
+CFLAGS-s_tan.c += -fno-builtin-tanl
+CFLAGS-s_tanh.c += -fno-builtin-tanhl
+CFLAGS-w_tgamma.c += -fno-builtin-tgammal
+CFLAGS-s_totalorder.c += -fno-builtin-totalorderl
+CFLAGS-s_totalordermag.c += -fno-builtin-totalordermagl
+CFLAGS-s_trunc.c += -fno-builtin-truncl
+CFLAGS-s_ufromfp.c += -fno-builtin-ufromfpl
+CFLAGS-s_ufromfpx.c += -fno-builtin-ufromfpxl
+CFLAGS-s_y0.c += -fno-builtin-y0l
+CFLAGS-s_y1.c += -fno-builtin-y1l
+CFLAGS-s_yn.c += -fno-builtin-ynl
 endif
 
 # These files quiet sNaNs in a way that is optimized away without
-- 
2.17.1