[gcc] Correct configure check so that it matches i686-pc-nacl

[gcc] Correct configure check so that it matches i686-pc-nacl

My earlier change was accidentally too strict, and did not match the
target configuration when it had been expanded from the argument in
"--target=nacl" to "i686-pc-nacl".

BUG=http://code.google.com/p/nativeclient/issues/detail?id=660
TEST=build full-gcc against nacl-glibc

Committed: http://code.google.com/p/nativeclient/source/detail?r=3098

[Mark Seaborn, 2010-08-24 16:29:25]

I thought I had forced a rebuild after changing the pattern from "*nacl*" to
"nacl*", but obviously I hadn't.

[khimg, 2010-08-24 17:54:02]

Oops.

LGTM