[clang][slh] Forward mSLH only to Clang CC1

[zbrid]

Summary

-mno-speculative-load-hardening isn't a cc1 option, therefore,
before this change:

clang -mno-speculative-load-hardening hello.cpp

would have the following error:

error: unknown argument: '-mno-speculative-load-hardening'

This change will only ever forward -mspeculative-load-hardening
which is a CC1 option based on which flag was passed to clang.

Also added a test that uses this option that fails if an error like the
above is ever thrown.

Thank you ericwf for help debugging and fixing this error.

[EricWF]

LGTM.

lib/Driver/ToolChains/Clang.cpp

if (A->getOption().matches(options::OPT_freroll_loops))
       CmdArgs.push_back("-freroll-loops");
 
   Args.AddLastArg(CmdArgs, options::OPT_fwritable_strings);
   Args.AddLastArg(CmdArgs, options::OPT_funroll_loops,
                   options::OPT_fno_unroll_loops);
 
   Args.AddLastArg(CmdArgs, options::OPT_pthread);
 
-  Args.AddLastArg(CmdArgs, options::OPT_mspeculative_load_hardening,
-                  options::OPT_mno_speculative_load_hardening);
+  if (Args.hasFlag(options::OPT_mspeculative_load_hardening, options::OPT_mno_speculative_load_hardening,
+                   false))
+    CmdArgs.push_back(Args.MakeArgString("-mspeculative-load-hardening"));
 
   RenderSSPOptions(TC, Args, CmdArgs, KernelOrKext);
 
   // Translate -mstackrealign
   if (Args.hasFlag(options::OPT_mstackrealign, options::OPT_mno_stackrealign,
                    false))
     CmdArgs.push_back(Args.MakeArgString("-mstackrealign"));
 

test/CodeGen/attr-speculative-load-hardening.c

 // RUN: %clang_cc1 -mspeculative-load-hardening -disable-llvm-passes -emit-llvm %s -o - | FileCheck %s -check-prefix=SLH
+// RUN: %clang -mno-speculative-load-hardening -S -emit-llvm %s -o - | FileCheck %s -check-prefix=NOSLH
 //
 // Check that we set the attribute on each function.
 
 int test1() {
   return 42;
 }
 // SLH: @{{.*}}test1{{.*}}[[SLH:#[0-9]+]]
 
 // SLH: attributes [[SLH]] = { {{.*}}speculative_load_hardening{{.*}} }
+
+// NOSLH: @{{.*}}test1{{.*}}[[NOSLH:#[0-9]+]]
+
+// NOSLH-NOT: attributes [[SLH]] = { {{.*}}speculative_load_hardening{{.*}} }