configure: Pass correct -target option to "cgcc" in the common case.

configure: Pass correct -target option to "cgcc" in the common case.

The "cgcc" script included with sparse guesses the target architecture
based on the host architecture instead of based on the GCC architecture.
This means that it often guesses wrong on biarch systems, e.g. my Linux
kernel is x86_64 but userspace is i686 and thus GCC targets i686 by
default.

This fixes the problem by passing an explicit "-target=i86" to cgcc if
GCC targets x86 or "-target=x86_64" if GCC targets x86_64.

Bug #6312.
Reported-by: Ethan Jackson <ethan@nicira.com>