Add --disable-sys-libs configure option.

This allows to disable the use of all system libraries with a single option
instead of having to use --with-{lib{png,jpeg,tiff},regex,zlib,expat}=builtin
or similar.

This is especially useful under OS X where we want to avoid the dependencies
on any locally installed homebrew or similar libraries.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76948 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

configure.in

@@ -401,6 +401,7 @@ if test "x$VENDOR" = "x"; then
 fi
 
 WX_ARG_DISABLE(all-features,[  --disable-all-features  disable all optional features to build minimal library], wxUSE_ALL_FEATURES)
+WX_ARG_DISABLE(sys-libs,    [  --disable-sys-libs      disable all use of system libraries, use only built-in ones], wxUSE_SYS_LIBS)
 
 if test "$wxUSE_ALL_FEATURES" = "no"; then
     dnl this is a bit ugly but currently we have no choice but to manually