ld: Compile 2 CTF tests with -O2

When GCC 12 is used to build binutils with -O0, the following 2 tests
failed:

FAIL: Conflicted data syms, partially indexed, stripped, with variables
FAIL: Conflicted data syms, partially indexed, stripped

Compile 2 tests with -O2 to avoid test failures.

	PR ld/29378
	* testsuite/ld-ctf/data-func-conflicted-vars.d: Compile with -O2.
	* testsuite/ld-ctf/data-func-conflicted.d: Likewise.