fix mingw detection: __GCC__ -> __GNUC__ (see also PR #1349)

Author: daanx

src/prim/windows/prim.c

@@ -876,7 +876,7 @@ static void NTAPI mi_win_main(PVOID module, DWORD reason, LPVOID reserved) {
     #pragma data_seg(".CRT$XIB")
       mi_crt_callback_t _mi_crt_callback_init[] = { &mi_crt_init };
     #pragma data_seg()
-  #elif defined(__GCC__)  // mingw
+  #elif defined(__GNUC__)  // mingw
     extern const IMAGE_TLS_DIRECTORY _tls_used;
     __attribute__((used)) static const void* const mi_tls_used_ref = &_tls_used; // pull in the CRT tls
     __attribute__((used, section(".CRT$XLB"))) PIMAGE_TLS_CALLBACK _mi_tls_callback_pre = &mi_tls_attach;
@@ -973,7 +973,7 @@ static void NTAPI mi_win_main(PVOID module, DWORD reason, LPVOID reserved) {
     #pragma data_seg(".CRT$XLY")
       PIMAGE_TLS_CALLBACK _mi_tls_callback_post[] = { &mi_tls_detach };
     #pragma data_seg()
-  #elif defined(__GCC__)  // mingw
+  #elif defined(__GNUC__)  // mingw
     extern const IMAGE_TLS_DIRECTORY _tls_used;
     __attribute__((used)) static const void* const mi_tls_used_ref = &_tls_used; // pull in the CRT tls
     __attribute__((used, section(".CRT$XLB"))) PIMAGE_TLS_CALLBACK _mi_tls_callback_pre  = &mi_tls_attach;
@@ -1047,7 +1047,7 @@ static void NTAPI mi_win_main(PVOID module, DWORD reason, LPVOID reserved) {
     #pragma data_seg(".CRT$XLY")
     PIMAGE_TLS_CALLBACK _mi_tls_callback_post[] = { &mi_win_main_detach };
     #pragma data_seg()
-  #elif defined(__GCC__)  // mingw
+  #elif defined(__GNUC__)  // mingw
     extern const IMAGE_TLS_DIRECTORY _tls_used;
     __attribute__((used)) static const void* const mi_tls_used_ref = &_tls_used; // pull in the CRT tls
     __attribute__((used, section(".CRT$XLB"))) PIMAGE_TLS_CALLBACK _mi_tls_callback_pre  = &mi_tls_attach;