cmake: use WINHTTP when USE_WINHTTP is specified
diff --git a/cmake/SelectWinHTTP.cmake b/cmake/SelectWinHTTP.cmake
index 1d950c9..667b400 100644
--- a/cmake/SelectWinHTTP.cmake
+++ b/cmake/SelectWinHTTP.cmake
@@ -1,4 +1,4 @@
-if(WIN32 AND WINHTTP)
+if(WIN32 AND USE_WINHTTP)
set(GIT_WINHTTP 1)
# Since MinGW does not come with headers or an import library for winhttp,