A couple of fixes for using Makefile.standalone on Mac.

Makefile.standalone

Index: Makefile.standalone
diff --git a/Makefile.standalone b/Makefile.standalone
index b0addadf436e4c3c5f3bf7078b3f643588056d14..2d3c0add27f26bda653b4761ad309b9c8407acea 100644
--- a/Makefile.standalone
+++ b/Makefile.standalone
@@ -18,9 +18,19 @@ LLVM_SRC_PATH ?= ../llvm
 LLVM_BIN_PATH ?= $(shell readlink -e \
 	../../out/llvm_i686_linux_work/Release+Asserts/bin)
 
+HOST_ARCH ?= x86
+ifeq ($(HOST_ARCH),x86_64)
+  HOST_FLAGS = -m64
+else
+  ifeq ($(HOST_ARCH),x86)
+    HOST_FLAGS = -m32
+  endif
+endif
+
 $(info -----------------------------------------------)
 $(info Using LLVM_SRC_PATH = $(LLVM_SRC_PATH))
 $(info Using LLVM_BIN_PATH = $(LLVM_BIN_PATH))
+$(info Using HOST_ARCH     = $(HOST_ARCH))
 $(info -----------------------------------------------)
 
 LLVM_CXXFLAGS := `$(LLVM_BIN_PATH)/llvm-config --cxxflags`
@@ -29,9 +39,11 @@ LLVM_LDFLAGS := `$(LLVM_BIN_PATH)/llvm-config --ldflags --libs`
 # It's recommended that CXX matches the compiler you used to build LLVM itself.
 OPTLEVEL := -O0
 CXX := g++
+
 CXXFLAGS := -Wall -Wextra -Werror -fno-rtti -fno-exceptions \
-	$(OPTLEVEL) -g $(LLVM_CXXFLAGS) -m32 -Wno-error=unused-parameter
-LDFLAGS := -m32
+	$(OPTLEVEL) -g $(LLVM_CXXFLAGS) $(HOST_FLAGS) \
+	-Wno-error=unused-parameter
+LDFLAGS := $(HOST_FLAGS)
 
 SRCS= \
 	IceCfg.cpp \