AIX: Test the -qlonglong option before use.

xlc provides "long long" unconditionally at C99-compatible language
levels, and this option provokes a warning.  The warning interferes with
"configure" tests that fail in response to any warning.  Notably, before
commit 85a2a8903f7e9151793308d0638621003aded5ae, it interfered with the
test for -qnoansialias.  Back-patch to 9.0 (all supported versions).
