Remove the config.h kludge and override vasprintf detection via HAVE_VASPRINTF.

include/compat.h

@@ -22,7 +22,7 @@ size_t HIDDEN strlcpy(char *, const char *, size_t);
 char HIDDEN *strcasestr(const char *, const char *);
 #endif
 
-#if !defined(HAVE_VASPRINTF) && !defined(_GNU_SOURCE)
+#ifndef HAVE_VASPRINTF
 int HIDDEN vasprintf(char **, const char *, va_list);
 #endif
 

include/xbps_api_impl.h

@@ -30,7 +30,7 @@
 #include <assert.h>
 #include <confuse.h>
 #define LIBXBPS_PRIVATE
-#include <xbps.h>
+#include "xbps.h"
 
 /*
  * By default all public functions have default visibility, unless