c-index-test/Makefile: Tweak USEDLIBS for cygwin. cygclang.dll is not linked to c-index-test yet.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@159499 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed