Add option to force filetype=asm for testing

Makefile.standalone

 # The following variables will likely need to be modified, depending on where
 # and how you built LLVM & Clang. They can be overridden in a command-line
 # invocation of make, like:
 #
 #   make LLVM_SRC_PATH=<path> LIBCXX_INSTALL_PATH=<path> CLANG_PATH=<path> \
 #        PNACL_BIN_PATH=<path> ...
 #
 
 # LLVM_SRC_PATH is the path to the root of the checked out source code. This
 # directory should contain the configure script, the include/ and lib/
@@ skipping 109 matching lines @@
   LD_EXTRA += -fsanitize=address
 endif
 
 ifdef MSAN
   # TODO(ascull): this has an as yet undiagnosed uninitialized memory access
   OBJDIR := $(OBJDIR)+MSan
   CXX_EXTRA += -fsanitize=memory
   LD_EXTRA += -fsanitize=memory
 endif
 
+ifdef FORCEASM
+  FORCEASM_FLAG = --filetype=asm
+  # With --filetype=asm and --sandbox, the llvm-mc assembler emits the lock and
+  # 16-bit prefixes in the "wrong" order, causing the validator to reject the
+  # resulting nexe.  So we just disable those tests for now.
+  FORCEASM_XTEST_EXCLUDES = -e x8632,sandbox,test_sync_atomic
+  FORCEASM_LIT_PARAM = --param=FORCEASM
+else
+  FORCEASM_FLAG =
+  FORCEASM_XTEST_EXCLUDES =
+  FORCEASM_LIT_PARAM =
+endif
+
 SB_OBJDIR := $(OBJDIR)+Sandboxed
 
 $(info -----------------------------------------------)
 $(info Using LLVM_SRC_PATH = $(LLVM_SRC_PATH))
 $(info Using SB_LLVM_PATH = $(SB_LLVM_PATH))
 $(info Using NACL_ROOT = $(NACL_ROOT))
 $(info Using TOOLCHAIN_ROOT = $(TOOLCHAIN_ROOT))
 $(info Using PNACL_TOOLCHAIN_ROOT = $(PNACL_TOOLCHAIN_ROOT))
 $(info Using PNACL_BIN_PATH = $(PNACL_BIN_PATH))
 $(info Using CLANG_PATH = $(CLANG_PATH))
@@ skipping 245 matching lines @@
 # Use runtime.is.built so that build-runtime.py is invoked only once
 # even in a parallel build.
 .INTERMEDIATE: runtime.is.built
 $(RT_OBJ): runtime.is.built
 runtime.is.built: $(RT_SRC) pydir/build-runtime.py
         @echo ================ Building Subzero runtime ================
         ./pydir/build-runtime.py -v --pnacl-root $(PNACL_TOOLCHAIN_ROOT)
 
 check-lit: $(OBJDIR)/pnacl-sz make_symlink
         PNACL_BIN_PATH=$(PNACL_BIN_PATH) \
-        $(LLVM_SRC_PATH)/utils/lit/lit.py -sv tests_lit
+        $(LLVM_SRC_PATH)/utils/lit/lit.py -sv tests_lit $(FORCEASM_LIT_PARAM)
 
 ifdef MINIMAL
 check-xtest: $(OBJDIR)/pnacl-sz make_symlink runtime
         @echo "Crosstests disabled, minimal build"
 else
 check-xtest: $(OBJDIR)/pnacl-sz make_symlink runtime
        # Do all native/sse2 tests, but only test_vector_ops for native/sse4.1.
        # For (slow) sandboxed tests, limit to Om1/sse4.1.
        # TODO(jpp): implement x8664 sandbox, then enable xtests.
        # TODO(jpp): reenable the x86-64 tests.
         ./pydir/crosstest_generator.py -v --lit \
           --toolchain-root $(TOOLCHAIN_ROOT) \
+          $(FORCEASM_FLAG) \
+          $(FORCEASM_XTEST_EXCLUDES) \
           -i x8632,native,sse2 \
           -i x8632,native,sse4.1,test_vector_ops \
           -i x8632,sandbox,sse4.1,Om1 \
           -i x8632,nonsfi,sse2,O2 \
           -i x8664,native,sse2 \
           -i x8664,native,sse4.1,test_vector_ops \
           -e x8664,sandbox,sse4.1,Om1 \
           -i arm32,neon \
           -e arm32,nonsfi \
           -e arm32,neon,test_vector_ops \
@@ skipping 45 matching lines @@
         +make -f Makefile.standalone format
 # Verify MINIMAL build, plus proper usage of REQUIRES in lit tests.
         +make -f Makefile.standalone \
           MINIMAL=1 check
 # Check that there are no g++ build errors or warnings.
         +make -f Makefile.standalone \
           GPLUSPLUS=1 compile_only
 # Check the x86 assembler unit tests.
         +make -f Makefile.standalone \
           DEBUG=1 CHECK_X86_ASM=1 check-unit
-# Run spec2k for x86-32.
+# Run lit tests, cross tests, unit tests, and spec2k/x86-32.
         +make -f Makefile.standalone \
           check check-spec
 # Build spec2k under -Om1/x86-32, to check for liveness errors.
         +make -f Makefile.standalone \
           SPECFLAGS='-Om1' SPECBUILDONLY=true check-spec
 # Run spec2k for x86-32 without advanced phi lowering.
         +make -f Makefile.standalone \
           SPECFLAGS='--sz=--phi-edge-split=0' check-spec
+# Run cross tests and lit tests to validate filetype=asm output.
+        +make -f Makefile.standalone \
+          FORCEASM=1 check-xtest check-lit
 # Build spec2k for arm32.
         +make -f Makefile.standalone \
           TARGET=arm32 SPECBUILDONLY=true check-spec
 # Build spec2k under -Om1/arm32.
         +make -f Makefile.standalone \
           TARGET=arm32 SPECFLAGS='-Om1' SPECBUILDONLY=true check-spec
 # Run a few spec2k tests for arm32 using qemu.
         +make -f Makefile.standalone \
           TARGET=arm32 ALLSPEC='176.gcc 181.mcf 254.gap' check-spec
 # Provide validation of user awesomeness!
@@ skipping 21 matching lines @@
         @echo See Subzero size breakdown in bloat/pnacl-sz.bloat.html
 
 docs:
         make -C docs -f Makefile.standalone
 
 clean:
         rm -rf pnacl-sz *.o $(OBJDIR) $(SB_OBJDIR) build/pnacl-sz.bloat.json
 
 clean-all: clean
         rm -rf build/  crosstest/Output/