[PATCH, Fortran] Skip gfortran.dg/PR100914.f90 on targets that don't provide quadmath.h

[Sandra Loosemore <sandra@codesourcery.com>]

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The testcase gfortran.dg/PR100914.f90 that I recently checked in 
(originally written by José Rui Faustino de Sousa) depends on the 
<quadmath.h> header file to obtain a typedef for __complex128.  It 
appears not to be possible to define an equivalent type in a portable 
way in the testcase itself (see 
https://gcc.gnu.org/onlinedocs/gcc-11.2.0/gcc/Floating-Types.html) so 
this patch skips the test entirely on targets where quadmath.h is not 
available.

The target-supports.exp change was cut-and-pasted from similar code in 
that file, but I haven't figured out how to test this change in a build 
that doesn't provide quadmath.h (e.g., my aarch64-linux-gnu toolchain 
build attempt croaked with an unrelated compilation error in glibc). 
Perhaps someone who previously encountered the FAILs on this testcase 
can confirm that it's skipped with this change?

-Sandra

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commit 41fe3b50b3d92931fc99ef15f86cc9299e0c617e
Author: Sandra Loosemore <sandra@codesourcery.com>
Date:   Sat Sep 4 18:36:39 2021 -0700

    Skip gfortran.dg/PR100914.f90 on targets that don't provide quadmath.h.
    
    This test uses the __complex128 type, which is provided by the
    <quadmath.h> header which may not be available on all targets.
    
    2021-09-04  Sandra Loosemore  <sandra@codesourcery.com>
    
    gcc/testsuite/
    
    	* lib/target-supports.exp (check_effective_target_quadmath_h):
    	New function.
    	* gfortran.dg/PR100914.f90: Use it.  Add comments.

diff --git a/gcc/testsuite/gfortran.dg/PR100914.f90 b/gcc/testsuite/gfortran.dg/PR100914.f90
index 64b3335..aff405a 100644
--- a/gcc/testsuite/gfortran.dg/PR100914.f90
+++ b/gcc/testsuite/gfortran.dg/PR100914.f90
@@ -1,7 +1,10 @@
 ! Fails on x86 targets where sizeof(long double) == 16.
 ! { dg-do run { xfail { { x86_64*-*-* i?86*-*-* } && longdouble128 } } }
-! { dg-additional-sources PR100914.c }
+! Requires Fortran support for __float128.
 ! { dg-require-effective-target fortran_real_c_float128 }
+! Requires __complex128 type from quadmath.h.
+! { dg-require-effective-target quadmath_h }
+! { dg-additional-sources PR100914.c }
 !
 ! Test the fix for PR100914
 ! 
diff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp
index ad8f011..072b776 100644
--- a/gcc/testsuite/lib/target-supports.exp
+++ b/gcc/testsuite/lib/target-supports.exp
@@ -8340,6 +8340,14 @@ proc check_effective_target_libc_has_complex_functions {} {
     }]
 }
 
+# Return true if this target has the quadmath.h header.
+
+proc check_effective_target_quadmath_h {} {
+    return [check_no_compiler_messages quadmath_h object {
+ #include <quadmath.h>
+    }]
+}
+
 # Return 1 if
 #   (a) an error of a few ULP is expected in string to floating-point
 #       conversion functions; and