[compiler-rt] Fix build errors with gcc

This patch fixes:

  compiler-rt/lib/builtins/crtbegin.c:11:18: error: missing binary
  operator before token "("

  compiler-rt/lib/builtins/crtbegin.c:53:18: error: missing binary
  operator before token "("

  compiler-rt/lib/builtins/crtbegin.c:124:18: error: missing binary
  operator before token "("

Author: kazutakahirata

compiler-rt/lib/builtins/crtbegin.c

@@ -8,6 +8,10 @@
 
 #include <stddef.h>
 
+#ifndef __has_feature
+# define __has_feature(x) 0
+#endif
+
 #if __has_feature(ptrauth_init_fini)
 #include <ptrauth.h>
 #endif