[gcc r16-540] libstdc++: Rewrite atomic builtin checks: Fix up 'GLIBCXX_ENABLE_BACKTRACE' check with 'size_t' [PR1

[Thomas Schwinge]

https://gcc.gnu.org/g:4589ccbed5cad42296d4d1810b61e8dec0dadf79

commit r16-540-g4589ccbed5cad42296d4d1810b61e8dec0dadf79
Author: Thomas Schwinge <tschwinge@baylibre.com>
Date:   Mon May 12 10:35:11 2025 +0200

    libstdc++: Rewrite atomic builtin checks: Fix up 'GLIBCXX_ENABLE_BACKTRACE' check with 'size_t' [PR119667]
    
    Fix-up for commit 86627faec10da53d7532805019e5296fcf15ac09
    "libstdc++: Rewrite atomic builtin checks [PR70560]", which, for example, for
    x86_64-pc-linux-gnu lost '-DHAVE_ATOMIC_FUNCTIONS=1' from 'BACKTRACE_CPPFLAGS'
    due to:
    
        configure:53554: checking for atomic builtins for libbacktrace
        configure:53587:  [...]/./gcc/xgcc -shared-libgcc -B[...]/./gcc -nostdinc++ -L[...]/x86_64-pc-linux-gnu/libstdc++-v3/src -L[...]/x86_64-pc-linux-gnu/libstdc++-v3/src/.libs -L[...]/x86_64-pc-linux-gnu/libstdc++-v3/libsupc++/.libs -B/x86_64-pc-linux-gnu/bin/ -B/x86_64-pc-linux-gnu/lib/ -isystem /x86_64-pc-linux-gnu/include -isystem /x86_64-pc-linux-gnu/sys-include    -o conftest -O0   conftest.cpp  >&5
        conftest.cpp: In function 'int main()':
        conftest.cpp:265:13: error: 'size_t' was not declared in this scope
          265 |             size_t s = 0;
              |             ^~~~~~
        conftest.cpp:1:1: note: 'size_t' is defined in header '<cstddef>'; this is probably fixable by adding '#include <cstddef>'
            1 | /* confdefs.h */
        conftest.cpp:273:31: error: 's' was not declared in this scope
          273 |             __atomic_store_n(&s, s, __ATOMIC_RELEASE);
              |                               ^
        configure:53587: $? = 1
        configure: failed program was:
        | /* confdefs.h */
        [...]
        | int
        | main ()
        | {
        |[...]
        |          size_t s = 0;
        |[...]
        |          // backtrace_atomic_store_size_t
        |          __atomic_store_n(&s, s, __ATOMIC_RELEASE);
        |[...]
        | }
        configure:53595: result: no
    
            PR libstdc++/70560
            PR libstdc++/119667
            libstdc++-v3/
            * acinclude.m4 (GLIBCXX_ENABLE_BACKTRACE): Use '__SIZE_TYPE__'
            instead of 'size_t'.
            * configure: Regenerate.

Diff:
---
 libstdc++-v3/acinclude.m4 | 4 ++--
 libstdc++-v3/configure    | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
index 204bed5b27be..d1ecb1ad9566 100644
--- a/libstdc++-v3/acinclude.m4
+++ b/libstdc++-v3/acinclude.m4
@@ -5304,7 +5304,7 @@ AC_DEFUN([GLIBCXX_ENABLE_BACKTRACE], [
 	[AC_TRY_LINK([], [
 	    int i = 0;
 	    int* p = &i;
-	    size_t s = 0;
+	    __SIZE_TYPE__ s = 0;
 	    // backtrace_atomic_load_pointer
 	    void* vp = __atomic_load_n(&p, __ATOMIC_ACQUIRE);
 	    // backtrace_atomic_load_int
@@ -5331,7 +5331,7 @@ int main()
 {
   int i = 0;
   int* p = &i;
-  size_t s = 0;
+  __SIZE_TYPE__ s = 0;
   // backtrace_atomic_load_pointer
   void* vp = __atomic_load_n(&p, __ATOMIC_ACQUIRE);
   // backtrace_atomic_load_int
diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
index 0529ff5708f1..d6891e544cfe 100755
--- a/libstdc++-v3/configure
+++ b/libstdc++-v3/configure
@@ -53568,7 +53568,7 @@ main ()
 
 	    int i = 0;
 	    int* p = &i;
-	    size_t s = 0;
+	    __SIZE_TYPE__ s = 0;
 	    // backtrace_atomic_load_pointer
 	    void* vp = __atomic_load_n(&p, __ATOMIC_ACQUIRE);
 	    // backtrace_atomic_load_int
@@ -53607,7 +53607,7 @@ int main()
 {
   int i = 0;
   int* p = &i;
-  size_t s = 0;
+  __SIZE_TYPE__ s = 0;
   // backtrace_atomic_load_pointer
   void* vp = __atomic_load_n(&p, __ATOMIC_ACQUIRE);
   // backtrace_atomic_load_int