Add option to build CMake against a system libuv

Create a CMAKE_USE_SYSTEM_LIBUV option.

Utilities/cmThirdParty.h.in

@@ -22,6 +22,7 @@
 #cmakedefine CMAKE_USE_SYSTEM_LIBLZMA
 #cmakedefine CMAKE_USE_SYSTEM_FORM
 #cmakedefine CMAKE_USE_SYSTEM_JSONCPP
+#cmakedefine CMAKE_USE_SYSTEM_LIBUV
 #cmakedefine CTEST_USE_XMLRPC
 
 #endif

Utilities/cm_uv.h

@@ -12,6 +12,12 @@
 #ifndef cm_uv_h
 #define cm_uv_h
 
+/* Use the libuv library configured for CMake.  */
+#include "cmThirdParty.h"
+#ifdef CMAKE_USE_SYSTEM_LIBUV
+#include <uv.h>
+#else
 #include <cmlibuv/include/uv.h>
+#endif
 
 #endif