Rename reference_output file (NFC)

[kkwli]

llvm_test_traditional() looks for the reference output filename without .cpp.

llvm-test-suite/cmake/modules/SingleMultiSource.cmake

Lines 112 to 124 in eed578a

	if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${name}.reference_output.${ENDIAN}-endian.${SIZE_SUFFIX})
	set(REFERENCE_OUTPUT ${name}.reference_output.${ENDIAN}-endian.${SIZE_SUFFIX})
	elseif(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${name}.reference_output.${SIZE_SUFFIX})
	set(REFERENCE_OUTPUT ${name}.reference_output.${SIZE_SUFFIX})
	elseif(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${name}.reference_output.${ENDIAN}-endian)
	set(REFERENCE_OUTPUT ${name}.reference_output.${ENDIAN}-endian)
	elseif(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${name}.reference_output.${TARGET_OS})
	set(REFERENCE_OUTPUT ${name}.reference_output.${TARGET_OS})
	elseif(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${name}.reference_output)
	set(REFERENCE_OUTPUT ${name}.reference_output)
	else()
	message("-- No reference output found for test ${name}")
	endif()

[kkwli]

@fhahn Ping