gdb/testsuite: Bump up `match_max'

gdb/testsuite: Bump up `match_max'

This fixes:

PASS: gdb.base/info-macros.exp: info macro  -a  --  FOO
ERROR: internal buffer is full.
UNRESOLVED: gdb.base/info-macros.exp: info macros 2
ERROR: internal buffer is full.
UNRESOLVED: gdb.base/info-macros.exp: info macros 3
ERROR: internal buffer is full.
UNRESOLVED: gdb.base/info-macros.exp: info macros 4
FAIL: gdb.base/info-macros.exp: info macros *$pc
ERROR: internal buffer is full.
UNRESOLVED: gdb.base/info-macros.exp: next
FAIL: gdb.base/info-macros.exp: info macros
ERROR: internal buffer is full.
UNRESOLVED: gdb.base/info-macros.exp: next
FAIL: gdb.base/info-macros.exp: info macros 6
ERROR: internal buffer is full.
UNRESOLVED: gdb.base/info-macros.exp: next
FAIL: gdb.base/info-macros.exp: info macros 7
ERROR: internal buffer is full.
UNRESOLVED: gdb.base/info-macros.exp: info macros info-macros.c:42 (PRMS
gdb/NNNN)

with the arm-eabi target tested on the i686-mingw32 host where GCC
defines enough macros to exhaust expect's 30000 characters of buffer
space.

	* lib/gdb.exp (default_gdb_init): Bump `match_max' up from
	30000 to 65536.