Revert driver: Don't warn about assembler flags being unused when not assembling

This reverts r365703 (git commit 101c1af)
and r365714.

This broke some autoconf-style assembler flags checks in the Linux
build:
ClangBuiltLinux/linux#598

llvm-svn: 365956

Author: rnk

clang/lib/Driver/ToolChains/Clang.cpp

@@ -3535,18 +3535,6 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   // Select the appropriate action.
   RewriteKind rewriteKind = RK_None;
 
-  // If CollectArgsForIntegratedAssembler() isn't called below, call it here
-  // with a dummy args list to mark assembler flags as used even when not
-  // running an assembler. Otherwise, clang would emit "argument unused"
-  // warnings for assembler flags when e.g. adding "-E" to flags while debugging
-  // something. That'd be somewhat inconvenient, and it's also inconsistent with
-  // most other flags -- we don't warn on -ffunction-sections not being used
-  // in -E mode either for example, even though it's not really used either.
-  if (!isa<AssembleJobAction>(JA)) {
-    ArgStringList DummyArgs;
-    CollectArgsForIntegratedAssembler(C, Args, DummyArgs, D);
-  }
-
   if (isa<AnalyzeJobAction>(JA)) {
     assert(JA.getType() == types::TY_Plist && "Invalid output type.");
     CmdArgs.push_back("-analyze");

clang/test/Driver/as-options.s

@@ -35,26 +35,3 @@
 // RUN:   | FileCheck %s
 
 // CHECK: "-I" "foo_dir"
-
-// Test that assembler options don't cause warnings when there's no assembler
-// stage.
-
-// RUN: %clang -mincremental-linker-compatible -E \
-// RUN:   -o /dev/null -x c++ %s 2>&1 \
-// RUN:   | FileCheck --check-prefix=WARN --allow-empty %s
-// RUN: %clang -mincremental-linker-compatible -E \
-// RUN:   -o /dev/null -x assembler-with-cpp %s 2>&1 \
-// RUN:   | FileCheck --check-prefix=WARN --allow-empty %s
-// RUN: %clang -mimplicit-it=always -target armv7-linux-gnueabi -E \
-// RUN:   -o /dev/null -x c++ %s 2>&1 \
-// RUN:   | FileCheck --check-prefix=WARN --allow-empty %s
-// RUN: %clang -mimplicit-it=always -target armv7-linux-gnueabi -E \
-// RUN:   -o /dev/null -x assembler-with-cpp %s 2>&1 \
-// RUN:   | FileCheck --check-prefix=WARN --allow-empty %s
-// RUN: %clang -Wa,-mbig-obj -target i386-pc-windows -E \
-// RUN:   -o /dev/null -x c++ %s 2>&1 \
-// RUN:   | FileCheck --check-prefix=WARN --allow-empty %s
-// RUN: %clang -Wa,-mbig-obj -target i386-pc-windows -E \
-// RUN:   -o /dev/null -x assembler-with-cpp %s 2>&1 \
-// RUN:   | FileCheck --check-prefix=WARN --allow-empty %s
-// WARN-NOT: unused