Add asprintf symbol for configure checks

git-svn-id: https://mingw-w64.svn.sourceforge.net/svnroot/mingw-w64@5819 4407c894-4637-0410-b4f5-ada5f102cad1
Split asprintf

git-svn-id: https://mingw-w64.svn.sourceforge.net/svnroot/mingw-w64@5820 4407c894-4637-0410-b4f5-ada5f102cad1