Fix GDB 7.7 support code

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@26711 3ad0048d-3df7-0310-abae-a5850022a9f2
 Add recognition of --enable-64-bit-bfd configure option, set GDB_CORE_ADDR_FORCE_64BITS conditional in this case

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@26712 3ad0048d-3df7-0310-abae-a5850022a9f2