Subzero: Add a separate check-xtest target to Makefile.standlone.

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> LLVM_BIN_PATH=<path> \
 #        LIBCXX_INSTALL_PATH=<path> CLANG_PATH=<path> \
 #        BINUTILS_BIN_PATH=<path> ...
 #
 
 # LLVM_SRC_PATH is the path to the root of the checked out source code. This
@@ skipping 198 matching lines @@
 $(RT_OBJ): runtime.is.built
 runtime.is.built: $(RT_SRC)
         @echo ================ Building Subzero runtime ================
         ./pydir/build-runtime.py -v --pnacl-root $(PNACL_TOOLCHAIN_ROOT)
 
 check-lit: $(OBJDIR)/pnacl-sz make_symlink
         LLVM_BIN_PATH=$(LLVM_BIN_PATH) \
         BINUTILS_BIN_PATH=$(BINUTILS_BIN_PATH) \
         $(LLVM_SRC_PATH)/utils/lit/lit.py -sv tests_lit
 
-check-unit: $(OBJDIR)/run_unittests
-        $(OBJDIR)/run_unittests
-
 ifdef MINIMAL
-check: check-lit check-unit runtime
-        @echo "Crosstests ignored, minimal build"
+check-xtest: $(OBJDIR)/pnacl-sz make_symlink runtime
+        @echo "Crosstests disabled, minimal build"
 else
-check: check-lit check-unit runtime
+check-xtest: $(OBJDIR)/pnacl-sz make_symlink runtime
        # Do all native/sse2 tests, but only test_vector_ops for native/sse4.1.
        # For (slow) sandboxed tests, limit to Om1/sse4.1.
         ./pydir/crosstest_generator.py -v --lit \
           -i native,sse2 -i native,sse4.1,test_vector_ops \
           -i sandbox,sse4.1,Om1
         LLVM_BIN_PATH=$(LLVM_BIN_PATH) \
         $(LLVM_SRC_PATH)/utils/lit/lit.py -sv crosstest/Output
 endif
 
+check-unit: $(OBJDIR)/run_unittests
+        $(OBJDIR)/run_unittests
+
+check: check-lit check-unit check-xtest
+
 FORMAT_BLACKLIST =
 # Add one of the following lines for each source file to ignore.
 FORMAT_BLACKLIST += ! -name IceParseInstsTest.cpp
 format:
         $(LLVM_BIN_PATH)/clang-format -style=LLVM -i \
         `find . -regex '.*\.\(c\|h\|cpp\)' $(FORMAT_BLACKLIST)`
 
 format-diff:
         git diff -U0 `git merge-base HEAD master` | \
         PATH=$(LLVM_BIN_PATH):$(PATH) \
         $(LLVM_SRC_PATH)/../clang/tools/clang-format/clang-format-diff.py \
         -p1 -style=LLVM -i
 
 bloat: make_symlink
         nm -C -S -l pnacl-sz | \
         bloat/bloat.py --nm-output=/dev/stdin syms > build/pnacl-sz.bloat.json
         @echo See Subzero size breakdown in bloat/pnacl-sz.bloat.html
 
 clean:
         rm -rf pnacl-sz *.o $(OBJDIR) build/pnacl-sz.bloat.json
 
 clean-all: clean
         rm -rf build/