Subzero: Improve the "make check-presubmit" target.

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 281 matching lines @@
 
 # Creates symbolic link so that testing is easier. Also runs
 # pnacl-sz to verify that the defines flags have valid values,
 # as well as describe the corresponding build attributes.
 make_symlink: $(OBJDIR)/pnacl-sz
         rm -rf pnacl-sz
         ln -s $(OBJDIR)/pnacl-sz
         @echo "Build Attributes:"
         @$(SHOW_BUILD_ATTS)
 
-.PHONY: all make_symlink runtime bloat sb docs
+.PHONY: all compile_only make_symlink runtime bloat sb docs
+
+compile_only: $(OBJS)
 
 $(OBJDIR)/pnacl-sz: $(OBJS)
         $(CXX) $(LDFLAGS) -o $@ $^ $(LLVM_LDFLAGS) \
           -Wl,-rpath=$(abspath $(LIBCXX_INSTALL_PATH)/lib)
 
 $(SB_OBJDIR)/pnacl-sz.x86-32.nexe: $(SB_OBJS)
         $(eval PNACL_SZ_BASE := $(patsubst %.nexe, %, $@))
         $(SB_CXX) $(SB_LDFLAGS) -o $(PNACL_SZ_BASE).nonfinal.pexe $^ \
           $(SB_LLVM_LDFLAGS)
         $(SB_TRANSLATE) -arch x86-32 $(PNACL_SZ_BASE).nonfinal.pexe -o $@ \
@@ skipping 109 matching lines @@
 %.spec2k: % $(OBJDIR)/pnacl-sz make_symlink runtime
         ./pydir/szbuild_spec2k.py -v --force \
           $(SPECFLAGS) --target=$(TARGETFLAG) $(SPEC) $<
         $(SPECBUILDONLY) || ( cd ../../../tests/spec2k; \
          ./run_all.sh RunTimedBenchmarks $(SETUP) train $< )
 
 check-spec: $(ALLSPEC:=.spec2k)
 
 check: check-lit check-unit check-xtest
 
-NPROCS := $(shell grep processor /proc/cpuinfo | wc -l)
-
-check-presubmit:
+check-presubmit presubmit:
+# Make sure clang-format gets run.
         +make -f Makefile.standalone format
-        git diff --quiet
+# Verify MINIMAL build, plus proper usage of REQUIRES in lit tests.
         +make -f Makefile.standalone \
           MINIMAL=1 check
+# Check the x86 assembler unit tests.
         +make -f Makefile.standalone \
           DEBUG=1 CHECK_X86_ASM=1 check-unit
+# Check that there are no g++ build errors or warnings.
+        +make -f Makefile.standalone clean
+        +make -f Makefile.standalone compile_only \
+          CXX=g++ STDLIB_FLAGS= \
+          LLVM_EXTRA_WARNINGS="-Wno-unknown-pragmas -Wno-unused-parameter \
+          -Wno-comment -Wno-enum-compare -Wno-strict-aliasing"
+        +make -f Makefile.standalone clean
+# Run spec2k for 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
+# 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
+# Verify that all changes are committed (including clang-format above).
+        git diff --quiet
+# Provide validation of user awesomeness!
         echo Success
 
 FORMAT_BLACKLIST =
 # Add one of the following lines for each source file to ignore.
 FORMAT_BLACKLIST += ! -name IceParseInstsTest.cpp
 FORMAT_BLACKLIST += ! -name IceParseTypesTest.cpp
 FORMAT_BLACKLIST += ! -name assembler_arm.h
 FORMAT_BLACKLIST += ! -name assembler_arm.cc
 format:
         $(CLANG_FORMAT_PATH)/clang-format -style=LLVM -i \
@@ skipping 12 matching lines @@
 
 docs:
         doxygen Doxyfile
         @echo See file://`pwd`/docs/html/index.html
 
 clean:
         rm -rf pnacl-sz *.o $(OBJDIR) $(SB_OBJDIR) build/pnacl-sz.bloat.json
 
 clean-all: clean
         rm -rf build/ docs/