Issue a linker error if TLS sections are not adjacent

Issue a linker error if TLS sections are not adjacent

Bad linker script may lead to TLS sections separated by non-TLS sections
in output.  This patch changes linker assert to a linker error to
provide better linker diagnosis.

	PR ld/16498
	* elf.c (_bfd_elf_map_sections_to_segments): Issue a linker error
	if TLS sections are not adjacent.