binutils: fix xtensa gas segfault with --text-section-literals

Building libgcc with TARGET_ABI flags results in assembler segfault on
xtensa, because code in sections .init and .fini emits literals w/o
.literal_position directive. This patch turns the segfault into assembly
error.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>