[libcxx] [test] Guard __has_include usage with a macro

[STL_MSFT]

Summary

There's a macro scheme already being used for has_feature etc. Use it for has_include too, which makes MSVC happy (it doesn't support __has_include yet, and unguarded use explodes horribly).

[EricWF]

LGTM. Although I would have thought the first half of the conjunction would have prevented MSVC's PP from seeing the __has_include.

I'll get to the rest of the patches tomorrow.

[EricWF]

r283260.

test/support/test_macros.h

 #define TEST_CONCAT(X, Y) TEST_CONCAT1(X, Y)
 
 #ifdef __has_feature
 #define TEST_HAS_FEATURE(X) __has_feature(X)
 #else
 #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
+#endif
+
 #ifdef __has_extension
 #define TEST_HAS_EXTENSION(X) __has_extension(X)
 #else
 #define TEST_HAS_EXTENSION(X) 0
 #endif
 
 #ifdef __has_builtin
 #define TEST_HAS_BUILTIN(X) __has_builtin(X)

 #elif __cplusplus <= 201402L
 # define TEST_STD_VER 14
 #else
 # define TEST_STD_VER 16    // current year; greater than current standard
 #endif
 #endif
 
 // Attempt to deduce GCC version
-#if defined(_LIBCPP_VERSION) && __has_include(<features.h>)
+#if defined(_LIBCPP_VERSION) && TEST_HAS_INCLUDE(<features.h>)
 #include <features.h>
 #define TEST_HAS_GLIBC
 #define TEST_GLIBC_PREREQ(major, minor) __GLIBC_PREREQ(major, minor)
 #endif
 
 /* Features that were introduced in C++14 */
 #if TEST_STD_VER >= 14
 #define TEST_HAS_EXTENDED_CONSTEXPR