PR15539: Record "evaluating if/elif condition" flag in the right place

The previous implementation missed the case where the elif condition was
evaluated from the context of an #ifdef that was false causing PR15539.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177345 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/Preprocessor/has_include.c b/test/Preprocessor/has_include.c
index 7cc67fa..131e519 100644
--- a/test/Preprocessor/has_include.c
+++ b/test/Preprocessor/has_include.c
@@ -176,3 +176,12 @@
 #else
   #error "__has_include failed (9)."
 #endif
+
+#if FOO
+#elif __has_include(<foo>)
+#endif
+
+// PR15539
+#ifdef FOO
+#elif __has_include(<foo>)
+#endif