Fix disabling of year 2038 support on 32-bit hosts by default

Commit e5f2f7d9 ("Disable year 2038 support on 32-bit hosts by
default") fixed a mismatch between 64-bit time_t in GDB and system headers
and 32-bit time_t in BFD.

However, since commit 862776f2 ("Finalized intl-update patches")
gnulib's year 2038 support has been accidentally re-enabled — causing
problems for 32-bit hosts again.  The commit split baseargs into
{h,b}baseargs, but this hasn't been done for the code that handles
--disable-year2038.

This patch restores the intended behaviour.  With this change, the number
of unexpected core files goes from 18 to 4.

Tested on armv8l-linux-gnueabihf.

Approved-By: Luis Machado <luis.machado@arm.com>