Check for 64bit atomic operations

May not be supported on some 32bit architectures.

```
/usr/lib/gcc-cross/m68k-linux-gnu/14/../../../../m68k-linux-gnu/bin/ld: ../../libruby-static.a(vm.o): in function `rbimpl_atomic_u64_set_relaxed':
/home/ubuntu/build/ruby/master/m68k-linux/../src/ruby_atomic.h:60:(.text+0x2468): undefined reference to `__atomic_store_8'
/usr/lib/gcc-cross/m68k-linux-gnu/14/../../../../m68k-linux-gnu/bin/ld: ../../libruby-static.a(vm.o): in function `rbimpl_atomic_u64_load_relaxed':
/home/ubuntu/build/ruby/master/m68k-linux/../src/ruby_atomic.h:43:(.text+0x2950):
undefined reference to `__atomic_load_8'
```

Author: nobu

configure.ac

@@ -1743,6 +1743,18 @@ AS_IF([test "$GCC" = yes], [
 		    [rb_cv_gcc_atomic_builtins=no])])
     AS_IF([test "$rb_cv_gcc_atomic_builtins" = yes], [
 	AC_DEFINE(HAVE_GCC_ATOMIC_BUILTINS)
+	AC_CACHE_CHECK([for 64bit __atomic builtins], [rb_cv_gcc_atomic_builtins_64], [
+	    AC_LINK_IFELSE([AC_LANG_PROGRAM([[@%:@include <stdint.h>
+			uint64_t atomic_var;]],
+			[[
+			    __atomic_load_n(&atomic_var, __ATOMIC_RELAXED);
+			    __atomic_store_n(&atomic_var, 0, __ATOMIC_RELAXED);
+			]])],
+			[rb_cv_gcc_atomic_builtins_64=yes],
+			[rb_cv_gcc_atomic_builtins_64=no])])
+	AS_IF([test "$rb_cv_gcc_atomic_builtins_64" = yes], [
+	    AC_DEFINE(HAVE_GCC_ATOMIC_BUILTINS_64)
+	])
     ])
 
     AC_CACHE_CHECK([for __sync builtins], [rb_cv_gcc_sync_builtins], [

ruby_atomic.h

@@ -39,7 +39,7 @@ rbimpl_atomic_load_relaxed(rb_atomic_t *ptr)
 static inline uint64_t
 rbimpl_atomic_u64_load_relaxed(const uint64_t *value)
 {
-#if defined(HAVE_GCC_ATOMIC_BUILTINS)
+#if defined(HAVE_GCC_ATOMIC_BUILTINS_64)
     return __atomic_load_n(value, __ATOMIC_RELAXED);
 #elif defined(_WIN32)
     uint64_t val = *value;
@@ -56,7 +56,7 @@ rbimpl_atomic_u64_load_relaxed(const uint64_t *value)
 static inline void
 rbimpl_atomic_u64_set_relaxed(uint64_t *address, uint64_t value)
 {
-#if defined(HAVE_GCC_ATOMIC_BUILTINS)
+#if defined(HAVE_GCC_ATOMIC_BUILTINS_64)
     __atomic_store_n(address, value, __ATOMIC_RELAXED);
 #elif defined(_WIN32)
     InterlockedExchange64(address, value);