[gcc r12-7225] libstdc++: Fix std::to_chars for IEEE128 long double

[gcc r12-7225] libstdc++: Fix std::to_chars for IEEE128 long double

[Jonathan Wakely]

https://gcc.gnu.org/g:813415650235b8ca42fe1afb3fcb0430e8628d30

commit r12-7225-g813415650235b8ca42fe1afb3fcb0430e8628d30
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Feb 10 14:06:27 2022 +0000

    libstdc++: Fix std::to_chars for IEEE128 long double
    
    The preprocessor check for _GLIBCXX_USE_FLOAT128 is the wrong condition,
    because when the compiler is built with --with-long-double-format=ieee
    configure determines that __float128 is the same as long double, and so
    should not be used. But we do want the std::to_chars overloads for
    __float128 in that case, because the floating_to_chars.cc file is built
    with -mabi=ibmlongdouble and so the __float128 overloads are actually
    the 'long double' ones for -mabi=ieeelongdouble code.
    
    This fixes missing definitions of the __float128 overloads of
    std::to_chars for --with-long-double-format=ieee builds. Without this,
    there are symbols present in the --with-long-double-abi=ibm build which
    are missing from the --with-long-double-abi=ieee build.
    
    libstdc++-v3/ChangeLog:
    
            * src/c++17/floating_to_chars.cc (FLOAT128_TO_CHARS): Depend on
            LONG_DOUBLE_ALT128_COMPAT instead of USE_FLOAT128.

Diff:
---
 libstdc++-v3/src/c++17/floating_to_chars.cc | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/libstdc++-v3/src/c++17/floating_to_chars.cc b/libstdc++-v3/src/c++17/floating_to_chars.cc
index 8da2f2385a0..5825e661bf4 100644
--- a/libstdc++-v3/src/c++17/floating_to_chars.cc
+++ b/libstdc++-v3/src/c++17/floating_to_chars.cc
@@ -76,16 +76,12 @@ extern "C" int __sprintfieee128(char*, const char*, ...);
 # define LONG_DOUBLE_KIND LDK_UNSUPPORTED
 #endif
 
-#if defined _GLIBCXX_USE_FLOAT128 && __FLT128_MANT_DIG__ == 113
+// For now we only support __float128 when it's the powerpc64 __ieee128 type.
+#if defined _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT && __FLT128_MANT_DIG__ == 113
 // Define overloads of std::to_chars for __float128.
 # define FLOAT128_TO_CHARS 1
 #endif
 
-// For now we only support __float128 when it's the powerpc64 __ieee128 type.
-#ifndef _GLIBCXX_LONG_DOUBLE_ALT128_COMPAT
-# undef FLOAT128_TO_CHARS
-#endif
-
 #ifdef FLOAT128_TO_CHARS
 using F128_type = __float128;
 #else