Check MSVC_RUNTIME only if MSVC is defined

On MinGW, WIN32 is set but not MSVC

cmake/FindOpenSSL.cmake

@@ -63,13 +63,13 @@ FIND_PATH(OPENSSL_INCLUDE_DIR
     include
 )
 
-IF(WIN32)
+IF(MSVC)
   if(${MSVC_RUNTIME} STREQUAL "static")
     set(MSVC_RUNTIME_SUFFIX "MT")
   else()
     set(MSVC_RUNTIME_SUFFIX "MD")
   endif()
-ENDIF(WIN32)
+ENDIF(MSVC)
 
 IF(ANDROID)
     FIND_LIBRARY(OPENSSL_LIBRARIES