gcc: Fix gcc-multilib-config comparison

gcc: Fix gcc-multilib-config comparison

Fix an issue on a multilib configuration that contains more then 1 multilib.

I.e. on MIPS64:

DEFAULTTUNE = "mips64"
MULTILIBS = "lib32n:mips64_n32 lib32:mips32"

While normally you'd use 'libn32', the above is legal.

With the startswith code, the system will look to expand the 'lib32' element
and find the 'lib32n' instead, and will result in a warning:

lib32 doesn't have a corresponding tune. Skipping...

Signed-off-by: Mark Hatle <mark.hatle@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>