Enable building LTO on WIN32.

Enable building the LTO library (.lib and.dll) and llvm-lto.exe on Windows with
MSVC and Mingw as well as re-enabling the associated test.

Patch by Greg Bedwell!

llvm-svn: 191823
diff --git a/llvm/tools/CMakeLists.txt b/llvm/tools/CMakeLists.txt
index 468d396..d8001e7 100644
--- a/llvm/tools/CMakeLists.txt
+++ b/llvm/tools/CMakeLists.txt
@@ -43,7 +43,7 @@
 add_llvm_tool_subdirectory(obj2yaml)
 add_llvm_tool_subdirectory(yaml2obj)
 
-if( NOT WIN32 )
+if( NOT CYGWIN )
   add_llvm_tool_subdirectory(lto)
   add_llvm_tool_subdirectory(llvm-lto)
 else()