Subzero makefile changes for linking a static llvm2ice nexe w/ LLVM build sys.

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> ...
 #
 
 # 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 79 matching lines @@
 
 LLVM_CXXFLAGS := `$(LLVM_BIN_PATH)/llvm-config --cxxflags`
 LLVM_LDFLAGS := `$(LLVM_BIN_PATH)/llvm-config --libs` \
                 `$(LLVM_BIN_PATH)/llvm-config --ldflags` \
                 `$(LLVM_BIN_PATH)/llvm-config --system-libs`
 
 # It's recommended that CXX matches the compiler you used to build LLVM itself.
 CCACHE := `command -v ccache`
 CXX := CCACHE_CPP2=yes $(CCACHE) $(CLANG_PATH)/clang++
 
-CXXFLAGS := $(LLVM_CXXFLAGS) -std=c++11 -Wall -Wextra -Werror -fno-rtti \
+CXXFLAGS := $(LLVM_CXXFLAGS) -std=gnu++11 -Wall -Wextra -Werror -fno-rtti \
         -fno-exceptions $(OPTLEVEL) $(ASSERTIONS) $(CXX_DEFINES) -g \
         $(HOST_FLAGS) -pedantic -Wno-error=unused-parameter \
         -I$(LIBCXX_INSTALL_PATH)/include/c++/v1 $(CXX_EXTRA)
 LDFLAGS := $(HOST_FLAGS) -L$(LIBCXX_INSTALL_PATH)/lib -Wl,--gc-sections \
         $(LD_EXTRA)
 
 SRCS = \
         assembler.cpp \
         assembler_ia32.cpp \
         IceCfg.cpp \
@@ skipping 123 matching lines @@
 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/