buildgcc: use ${GDB_DIR} instead of gdb-${GDB_VERSION}

Bring gdb in sync with all other build targets.

Change-Id: I9c478947a00f044edf910a91d876bbf486a791cf
Signed-off-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-on: http://review.coreboot.org/10488
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins)
Reviewed-by: Alexander Couzens <lynxis@fe80.eu>
1 file changed