Build: Disable compiler warnings for zlib-ng build

The zlib-ng build breaks with some of the compiler warnings that our CI
build tests.  We assume that compiler warnings in upstream software are
the concern of the upstream maintainers anyhow.

unix/Xvnc/lib/CMakeLists.txt

@@ -15,7 +15,7 @@ if(TVNC_ZLIBNG)
 		CMAKE_ARGS
 			-DBUILD_SHARED_LIBS=0
 			-DCMAKE_C_COMPILER=${CMAKE_C_COMPILER}
-			-DCMAKE_C_FLAGS=${CMAKE_C_FLAGS}
+			"-DCMAKE_C_FLAGS=${CMAKE_C_FLAGS} -w"
 			-DCMAKE_C_FLAGS_DEBUG=${CMAKE_C_FLAGS_DEBUG}
 			-DCMAKE_C_FLAGS_MINSIZEREL=${CMAKE_C_FLAGS_MINSIZEREL}
 			-DCMAKE_C_FLAGS_RELEASE=${CMAKE_C_FLAGS_RELEASE}