Don't warn on unused -fno-lto.

It is somewhat common for CFLAGS to be used with .s files. We were
already ignoring -flto. This patch just does the same for -fno-lto.

llvm-svn: 225093
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index 90d1acc..93027df 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -3379,9 +3379,10 @@
     D.Diag(diag::warn_ignored_gcc_optimization) << (*it)->getAsString(Args);
   }
 
-  // Don't warn about unused -flto.  This can happen when we're preprocessing or
-  // precompiling.
+  // Don't warn about unused -f(no-)?lto.  This can happen when we're preprocessing,
+  // precompiling or assembling.
   Args.ClaimAllArgs(options::OPT_flto);
+  Args.ClaimAllArgs(options::OPT_fno_lto);
 
   Args.AddAllArgs(CmdArgs, options::OPT_R_Group);
   Args.AddAllArgs(CmdArgs, options::OPT_W_Group);