[clang] Unify -mspeculative-load-hardening as a benign compiler option

Before this patch, compilations using modules &
-mspeculative-load-hardening because of a configuration mismatch because
it was not consistent whether this option impacts module compatibility.

This repairs it by always treating it as benign. This was determined by
checking if the option enables any kind of preprocessor checks and
comparing how the compiler handles a similiar option that impacts codegen
(-fvisibility=hidden) but is more widely used.

Author: cyndyishida

clang/include/clang/Basic/LangOptions.def

@@ -454,7 +454,7 @@ LANGOPT(BranchTargetEnforcement, 1, 0, NotCompatible, "Branch-target enforcement
 LANGOPT(BranchProtectionPAuthLR, 1, 0, NotCompatible, "Use PC as a diversifier using PAuthLR NOP instructions.")
 LANGOPT(GuardedControlStack, 1, 0, NotCompatible, "Guarded control stack enabled")
 
-LANGOPT(SpeculativeLoadHardening, 1, 0, NotCompatible, "Speculative load hardening enabled")
+LANGOPT(SpeculativeLoadHardening, 1, 0, Benign, "Speculative load hardening enabled")
 
 LANGOPT(RelativeCXXABIVTables, 1, 0, NotCompatible,
         "Use an ABI-incompatible v-table layout that uses relative references")

clang/test/ClangScanDeps/strip-codegen-args.m

@@ -16,6 +16,7 @@
 // CHECK-NOT:          "-flto"
 // CHECK-NOT:          "-fno-autolink"
 // CHECK-NOT:          "-mrelax-relocations=no"
+// CHECK-NOT:          "-mspeculative-load-hardening"
 // CHECK:            ]
 // CHECK:            "name": "A"
 // CHECK:          }
@@ -39,6 +40,11 @@
     "command": "clang -Imodules/A -fmodules -fmodules-cache-path=DIR/module-cache -fimplicit-modules -O2 -flto=full -fsyntax-only DIR/t3.m",
     "file": "DIR/t2.m"
   }
+  {
+    "directory": "DIR",
+    "command": "clang -Imodules/A -fmodules -fmodules-cache-path=DIR/module-cache -fimplicit-modules -O2 -mspeculative-load-hardening -fsyntax-only DIR/t3.m",
+    "file": "DIR/t3.m"
+  }
 ]
 
 //--- modules/A/module.modulemap