Fix stdint.h dependency in slvs.h.

Since SolveSpace's config.h is not exported, we cannot depend
on HAVE_C99_INTEGER_TYPES or similar variables. It's simplest
to just define it from scratch in the same way as MSVC does.

include/slvs.h

@@ -24,8 +24,10 @@
 extern "C" {
 #endif
 
-#if defined(WIN32) && !defined(HAVE_C99_INTEGER_TYPES)
-typedef UINT32 uint32_t;
+#ifdef _MSC_VER
+typedef unsigned __int32 uint32_t;
+#else
+#include <stdint.h>
 #endif
 
 typedef uint32_t Slvs_hParam;