LoongArch: testsuite: Disable stack protector for got-load.C

When building GCC with --enable-default-ssp, the stack protector is
enabled for got-load.C, causing additional GOT loads for
__stack_chk_guard.  So mem/u will be matched more than 2 times and the
test will fail.

Disable stack protector to fix this issue.

gcc/testsuite:

	* g++.target/loongarch/got-load.C (dg-options): Add
	-fno-stack-protector.