PR ld/24709 [arm] linker crash and assertion failure with CMSE

PR ld/24709 [arm] linker crash and assertion failure with CMSE

As discussed in the PR, we do not support the case where CMSE stubs
are inserted too far from their destination. This would require an
intermediate long-branch stub, which is tricky in this context.

Instead of crashing, this patch emit an error message and exits.

2019-07-02  Christophe Lyon  <christophe.lyon@linaro.org>

	* bfd/elf32-arm.c (CMSE_STUB_NAME): New define.
	(elf32_arm_get_stub_entry): Do not try to emit long-branch stubs
	for CMSE stubs.
	(arm_dedicated_stub_output_section_name): Use CMSE_STUB_NAME.

Change-Id: I6d4e1c0fdee6bb9f4b07e5e1b46700b5ba31c62e