s390: Do not replace brcth referencing undefined weak symbol

s390: Do not replace brcth referencing undefined weak symbol

Branch Relative on Count High (brcth) is a conditional branch relative
instruction. It is not guaranteed that it only appears within loops
that sooner or later will take the branch. It may very well be used to
check a condition that will prevent the branch from ever being taken.

bfd/
	* elf64-s390.c (elf_s390_relocate_section): Do not replace brcth
	referencing undefined weak symbol with a trap.

ld/
	* testsuite/ld-s390/weakundef-1.s: Update test case accordingly.
	* testsuite/ld-s390/weakundef-1.dd: Likewise.

Fixes: 896a639babe2 ("s390: Avoid reloc overflows on undefined weak symbols")
Signed-off-by: Jens Remus <jremus@linux.ibm.com>