msys2: don't try to link msys librt and libpthread

In cmake on Win32, don't try to find librt or libpthread using
find_library(), and on mingw just include -lpthread.

For some reason the msys versions of librt and libpthread were being
picked up when find_library() was being used.

CMakeLists.txt

@@ -253,16 +253,23 @@ add_definitions(-DPKGDATADIR="${CMAKE_INSTALL_FULL_DATADIR}/vbam" -DPACKAGE=)
 
 if(ENABLE_LINK)
     # IPC linking code needs sem_timedwait which can be either in librt or pthreads
-    find_library(RT_LIB rt)
-    if(RT_LIB)
-       set(CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES} ${RT_LIB})
-       set(VBAMCORE_LIBS ${VBAMCORE_LIBS} ${RT_LIB})
+    if(NOT WIN32)
+        find_library(RT_LIB rt)
+        if(RT_LIB)
+           set(CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES} ${RT_LIB})
+           set(VBAMCORE_LIBS ${VBAMCORE_LIBS} ${RT_LIB})
+        endif()
     endif()
 
-    find_library(PTHREAD_LIB pthread)
-    if(PTHREAD_LIB)
-       set(CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES} ${PTHREAD_LIB})
-       set(VBAMCORE_LIBS ${VBAMCORE_LIBS} ${PTHREAD_LIB})
+    if(NOT WIN32)
+        find_library(PTHREAD_LIB pthread)
+        if(PTHREAD_LIB)
+           set(CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES} ${PTHREAD_LIB})
+           set(VBAMCORE_LIBS ${VBAMCORE_LIBS} ${PTHREAD_LIB})
+        endif()
+    elseif(MINGW)
+       set(CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES} -lpthread)
+       set(VBAMCORE_LIBS ${VBAMCORE_LIBS} -lpthread)
     endif()
 
     include(CheckFunctionExists)