[glibc] ldbl-opt: Fix -mlong-double-128 configure test for Clang

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=e7a14f03b8d5e34e8ac46db6c377da5c66a3ec2a

commit e7a14f03b8d5e34e8ac46db6c377da5c66a3ec2a
Author: Matt Turner <[email protected]>
Date:   Sun Jul 26 00:27:37 2026 -0400

    ldbl-opt: Fix -mlong-double-128 configure test for Clang
    
    The check for -mlong-double-128 support wrapped its test code in
    AC_LANG_PROGRAM, which places the body inside main().  The body defines
    a function, so it became a nested function definition -- a GCC extension
    that Clang does not implement, making the test fail (and thus the whole
    build error out) with Clang even though it supports -mlong-double-128.
    
    Use AC_LANG_SOURCE so the function is defined at file scope, matching the
    pattern already used by the powerpc64le compiler checks, and regenerate
    configure.
    
    Reviewed-by: Sam James <[email protected]>

Diff:
---
 sysdeps/ieee754/ldbl-opt/configure    | 7 -------
 sysdeps/ieee754/ldbl-opt/configure.ac | 2 +-
 2 files changed, 1 insertion(+), 8 deletions(-)

diff --git a/sysdeps/ieee754/ldbl-opt/configure b/sysdeps/ieee754/ldbl-opt/configure
old mode 100644
new mode 100755
index bc6552da0b..7769cc9781
--- a/sysdeps/ieee754/ldbl-opt/configure
+++ b/sysdeps/ieee754/ldbl-opt/configure
@@ -13,17 +13,10 @@ CFLAGS="$CFLAGS -mlong-double-128"
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
-int
-main (void)
-{
-
 #ifndef __LONG_DOUBLE_128__
 # error "compiler did not predefine __LONG_DOUBLE_128__ as expected"
 #endif
 long double foobar (long double x) { return x; }
-  ;
-  return 0;
-}
 _ACEOF
 if ac_fn_c_try_compile "$LINENO"
 then :
diff --git a/sysdeps/ieee754/ldbl-opt/configure.ac b/sysdeps/ieee754/ldbl-opt/configure.ac
index 70e3b32dc6..1c500ad581 100644
--- a/sysdeps/ieee754/ldbl-opt/configure.ac
+++ b/sysdeps/ieee754/ldbl-opt/configure.ac
@@ -6,7 +6,7 @@ AC_CACHE_CHECK(whether $CC $CFLAGS supports -mlong-double-128,
 	       libc_cv_mlong_double_128, [dnl
 save_CFLAGS="$CFLAGS"
 CFLAGS="$CFLAGS -mlong-double-128"
-AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]], [[
+AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
 #ifndef __LONG_DOUBLE_128__
 # error "compiler did not predefine __LONG_DOUBLE_128__ as expected"
 #endif