Fresh build on OS X Mountain Lion yields "warning: no debug symbols in executable (-arch x86_64)" on compiles

[johnnyw]

Version info for clang++:

Apple LLVM version 4.2 (clang-425.0.28) (based on LLVM 3.2svn)
Target: x86_64-apple-darwin12.4.1
Thread model: posix

OS X version: 10.8.4

Steps to reproduce:
Download and unzip http://static.rust-lang.org/dist/rust-0.7.tar.gz
in rust-0.7 directory:
./configure
make
make install

Then compile a simple rust program (hello world will do):
rustc hello.rs

"warning: no debug symbols in executable (-arch x86_64)" is displayed, instead of silently succeeding.

[metajack]

This is a dupe of #3495