Allows functions doing selftests to take parameters with names like
"actual".

2017-12-07  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* selftest.h (ASSERT_TRUE_AT, ASSERT_FALSE_AT, ASSERT_EQ_AT)
	(ASSERT_NE, ASSERT_PRED1): Add underscores to local variable names
	* selftest-rtl.h (ASSERT_RTX_EQ, ASSERT_RTX_PTR_EQ): Likewise.

From-SVN: r255473