Replace the native OS X assembler (/usr/bin/as) by a script which calls the clang assembler. (http://old.nabble.com/Re%3a-gcc,-as,-AVX,-binutils-and-MacOS-X-10.7-p32584737.html)

as

#!/bin/sh 
HAS_INPUT_FILE=0 
ARGS=$@ 
while [ $# -ne 0 ]; do 
        ARG=$1 
        # Skip options 
        if [ $ARG == "-arch" ] || [ $ARG == "-o" ]; then 
                # Skip next token 
                shift 
                shift 
                continue 
        fi 

        if [ `echo $ARG | head -c1` == "-" ]; then 
                shift 
                continue 
        fi 

        HAS_INPUT_FILE=1 
        break 
done 

if [ $HAS_INPUT_FILE -eq 1 ]; then 
        clang -c -x assembler $ARGS 
else 
        clang -c -x assembler $ARGS - 
fi 

Thanks a bunch for this!
When I use it with include flags (e.g. g++ -I/opt/local/include/), then I get warnings such as
clang: warning: argument unused during compilation: '-I /opt/local/include/'
Would it be possible to filter out includes from $ARGS before passing them into clang?

Thanks this solved my problem! I had installing xgboost which gave me the following error: FATAL:/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../libexec/as/x86_64/as: I don't understand 'm' flag!
I noticed something was wrong with the assembler since running $as --version also gave me a similar error. Replacing /usr/bin/as with the above solved the problem.