Stop wrapping __has_include in another macro

Summary:
This is not guaranteed to work since the characters after '__has_include('
have special lexing rules that can't possibly be applied when
__has_include is generated by a macro. It also breaks the crash reproducers
generated by -frewrite-includes (see https://llvm.org/pr37990).

Reviewers: EricWF, rsmith, mclow.lists
Reviewed By: mclow.lists
Differential Revision: https://reviews.llvm.org/D49067

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@337824 91177308-0d34-0410-b5e6-96231b3b80d8

test/support/test_macros.h

@@ -27,10 +27,8 @@
 #define TEST_HAS_FEATURE(X) 0
 #endif
 
-#ifdef __has_include
-#define TEST_HAS_INCLUDE(X) __has_include(X)
-#else
-#define TEST_HAS_INCLUDE(X) 0
+#ifndef __has_include
+#define __has_include(...) 0
 #endif
 
 #ifdef __has_extension
@@ -90,7 +88,7 @@
 #endif
 
 // Attempt to deduce GCC version
-#if defined(_LIBCPP_VERSION) && TEST_HAS_INCLUDE(<features.h>)
+#if defined(_LIBCPP_VERSION) && __has_include(<features.h>)
 #include <features.h>
 #define TEST_HAS_GLIBC
 #define TEST_GLIBC_PREREQ(major, minor) __GLIBC_PREREQ(major, minor)