[GOLD] justsyms_exec test fail on powerpc64

This test fails on powerpc64le due to the justsyms_lib being built
with exported_data at 0x2010000, apparently due to the powerpc target
code generating an empty relro .branch_lt section.  Since the test
relies on the library having exported_data at 0x2000000, avoid the
problem by linking with -z norelro.  Also, the test doesn't need to
avoid checking the function symbol on powerpc elfv2.

	* testsuite/Makefile.am (justsyms_lib): Link with -z norelro.
	* testsuite/Makefile.in: Regenerate.
	* testsuite/justsyms_exec.c (main): Do check exported_func
	on PowerPC64 ELFv2.