Valid linker options should be treated for elf consistently
with the linux-gnu target.

I'm not sure about the undocumented -h option (blindly copied
LINUX_TARGET_LINK_SPEC from aarch64-linux without the
dynamic-linker flag).

(Not passing -shared can cause broken vdso.so in the linux
kernel when it is built with the elf toolchain.)

2015-07-22  Szabolcs Nagy  <szabolcs.nagy@arm.com>

	* config/aarch64/aarch64-elf-raw.h (LINK_SPEC): Handle -h, -static,
	-shared, -symbolic, -rdynamic.