[binutils-gdb] Make amd64_x32_init_abi and amd64_init_abi argument constant

[sergiodj+buildbot@sergiodj.net]

*** TEST RESULTS FOR COMMIT a04b53379a18c66376b4130dc3b4936e6433a0e5 ***

Author: Yao Qi <yao.qi@linaro.org>
Branch: master
Commit: a04b53379a18c66376b4130dc3b4936e6433a0e5

Make amd64_x32_init_abi and amd64_init_abi argument constant

gdb:

2017-07-25  Yao Qi  <yao.qi@linaro.org>

	* amd64-tdep.c (amd64_init_abi): Make argument default_tdesc
	constant.
	(amd64_x32_init_abi): Likewise.
	* amd64-tdep.h (amd64_init_abi): Update declaration.
	(amd64_x32_init_abi): Likewise.