On Xcode's clang on OS X, $cc --version will output a 'Configured with:'
line to stderr, which clobbers the configure script output. As this line
serves no further purpose, it should be silenced.

The same applies to apple-gcc 4.2.1, which complains that it can not
understand the kernel version it is running on.
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>