test_vars: also check @IS_MSVC@ content
test_vars: also check @IS_MSVC@ content

On autotools if @IS_MSVC@ is not defined, it is left as a string
literal, instead of being nothing. Because of that, the content
is now also checked. For CMake and MSVC, @IS_MSVC@ will be '1'.
Otherwise, it can be anything else.

git-svn-id: caee63afe878fe2ec7dbba394a86c9654d9110ca@1045 64e312b2-a51f-0410-8e61-82d0ca0eb02a

svn2github/check,svn2github/check,dashaomai/check-code,dashaomai/check-code,dashaomai/check-code,svn2github/check,dashaomai/check-code,svn2github/check,svn2github/check