[libc++] Don't workaround GCC issue on non-GCC compilers

Differential Revision: https://reviews.llvm.org/D138438

Author: ldionne

libcxx/include/limits.h

@@ -43,13 +43,8 @@
 #  pragma GCC system_header
 #endif
 
-#ifndef __GNUC__
+#ifdef _LIBCPP_COMPILER_GCC
 
-#  if __has_include_next(<limits.h>)
-#    include_next <limits.h>
-#  endif
-
-#else
 // GCC header limits.h recursively includes itself through another header called
 // syslimits.h for some reason. This setup breaks down if we directly
 // #include_next GCC's limits.h (reasons not entirely clear to me).
@@ -64,6 +59,13 @@
 // Get the ISO C defines
 #undef _GCC_LIMITS_H_
 #include_next <limits.h>
-#endif // __GNUC__
+
+#else
+
+#  if __has_include_next(<limits.h>)
+#    include_next <limits.h>
+#  endif
+
+#endif // _LIBCPP_COMPILER_GCC
 
 #endif // _LIBCPP_LIMITS_H