[clang][slh] add attribute for speculative load hardening

Summary:
Resubmit this with no changes because I think the build was broken
by a different diff.
-----
The prior diff had to be reverted because there were two tests
that failed. I updated the two tests in this diff

clang/test/Misc/pragma-attribute-supported-attributes-list.test
clang/test/SemaCXX/attr-speculative-load-hardening.cpp

----- Summary from Previous Diff (Still Accurate) -----

LLVM IR already has an attribute for speculative_load_hardening. Before
this commit, when a user passed the -mspeculative-load-hardening flag to
Clang, every function would have this attribute added to it. This Clang
attribute will allow users to opt into SLH on a function by function basis.

This can be applied to functions and Objective C methods.

Reviewers: chandlerc, echristo, kristof.beyls, aaron.ballman

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D54915

llvm-svn: 347701
diff --git a/clang/test/Misc/pragma-attribute-supported-attributes-list.test b/clang/test/Misc/pragma-attribute-supported-attributes-list.test
index 0a54c6c..0aa923d 100644
--- a/clang/test/Misc/pragma-attribute-supported-attributes-list.test
+++ b/clang/test/Misc/pragma-attribute-supported-attributes-list.test
@@ -2,7 +2,7 @@
 
 // The number of supported attributes should never go down!
 
-// CHECK: #pragma clang attribute supports 129 attributes:
+// CHECK: #pragma clang attribute supports 130 attributes:
 // CHECK-NEXT: AMDGPUFlatWorkGroupSize (SubjectMatchRule_function)
 // CHECK-NEXT: AMDGPUNumSGPR (SubjectMatchRule_function)
 // CHECK-NEXT: AMDGPUNumVGPR (SubjectMatchRule_function)
@@ -116,6 +116,7 @@
 // CHECK-NEXT: ScopedLockable (SubjectMatchRule_record)
 // CHECK-NEXT: Section (SubjectMatchRule_function, SubjectMatchRule_variable_is_global, SubjectMatchRule_objc_method, SubjectMatchRule_objc_property)
 // CHECK-NEXT: SetTypestate (SubjectMatchRule_function_is_member)
+// CHECK-NEXT: SpeculativeLoadHardening (SubjectMatchRule_function, SubjectMatchRule_objc_method)
 // CHECK-NEXT: SwiftContext (SubjectMatchRule_variable_is_parameter)
 // CHECK-NEXT: SwiftErrorResult (SubjectMatchRule_variable_is_parameter)
 // CHECK-NEXT: SwiftIndirectResult (SubjectMatchRule_variable_is_parameter)