[PAC][compiler-rt] Do not use __has_feature with non-clang

See compile failure with gcc:
llvm#96478 (comment)

The `__has_feature` directive was not supported in gcc until ~ Nov 2023
gcc-mirror/gcc@06280a9

Author: kovdan01

compiler-rt/lib/builtins/crtbegin.c

@@ -54,6 +54,7 @@ static void __attribute__((used)) __do_init(void) {
 }
 
 #ifdef CRT_HAS_INITFINI_ARRAY
+#ifdef __clang__
 #if __has_feature(ptrauth_init_fini)
 // TODO: use __ptrauth-qualified pointers when they are supported on clang side
 #if __has_feature(ptrauth_init_fini_address_discrimination)
@@ -70,6 +71,10 @@ __attribute__((section(".init_array"), used)) static void *__init =
 __attribute__((section(".init_array"),
                used)) static void (*__init)(void) = __do_init;
 #endif
+#else
+__attribute__((section(".init_array"),
+               used)) static void (*__init)(void) = __do_init;
+#endif
 #elif defined(__i386__) || defined(__x86_64__)
 __asm__(".pushsection .init,\"ax\",@progbits\n\t"
         "call __do_init\n\t"
@@ -125,6 +130,7 @@ static void __attribute__((used)) __do_fini(void) {
 }
 
 #ifdef CRT_HAS_INITFINI_ARRAY
+#ifdef __clang__
 #if __has_feature(ptrauth_init_fini)
 // TODO: use __ptrauth-qualified pointers when they are supported on clang side
 #if __has_feature(ptrauth_init_fini_address_discrimination)
@@ -141,6 +147,10 @@ __attribute__((section(".fini_array"), used)) static void *__fini =
 __attribute__((section(".fini_array"),
                used)) static void (*__fini)(void) = __do_fini;
 #endif
+#else
+__attribute__((section(".fini_array"),
+               used)) static void (*__fini)(void) = __do_fini;
+#endif
 #elif defined(__i386__) || defined(__x86_64__)
 __asm__(".pushsection .fini,\"ax\",@progbits\n\t"
         "call __do_fini\n\t"