Make platform designation precise.

[suikan4github]

Currently, we designate OS as follows when delete gcda data :

template_application/test/CMakeLists.txt

Lines 24 to 32 in 559a57b

	if(NOT MSVC)
	# Delete the gcov data file before linking. Otherwise, we will get many errors.
	add_custom_command(
	TARGET ${TEST_EXECUTABLE_NAME} PRE_LINK
	COMMAND find . -name "*.gcda" -delete
	COMMENT "Deleting *.gcda files under ${CMAKE_BINARY_DIR}"
	WORKING_DIRECTORY ${CMAKE_BINARY_DIR}
	VERBATIM)
	endif()

This is OK when the target is MSVC on the WIndows. But fail if the target is GCC on the WIndows. Perhaps, we should change as followings :

if (UNIX)
elseif (WIN32)
endif()

In Windows, the following command can work in both Powershell and command.com :

powershell -c remove-item -include *.gcda -recurse