[clang][slh] Add test for SLH feature checking macro

Summary:
I forgot to include a test in this commit:
https://reviews.llvm.org/rG379e68a763097bed55556c6dc7453e4b732e3d68

Here's the test. It passes after that commit and fails before that commit.

Reviewed By: mattdr

Differential Revision: https://reviews.llvm.org/D79894

Author: zbrid

clang/test/Lexer/has_feature_speculative_load_hardening.cpp

@@ -0,0 +1,15 @@
+// RUN: %clang -E -mspeculative-load-hardening %s -o - | FileCheck --check-prefix=CHECK-SLH %s
+// RUN: %clang -E -mno-speculative-load-hardening %s -o - | FileCheck --check-prefix=CHECK-NOSLH %s
+// RUN: %clang -E %s -o - | FileCheck --check-prefix=CHECK-DEFAULT %s
+
+#if __has_feature(speculative_load_hardening)
+int SpeculativeLoadHardeningEnabled();
+#else
+int SpeculativeLoadHardeningDisabled();
+#endif
+
+// CHECK-SLH: SpeculativeLoadHardeningEnabled
+
+// CHECK-NOSLH: SpeculativeLoadHardeningDisabled
+
+// CHECK-DEFAULT: SpeculativeLoadHardeningDisabled