https://bugs.webkit.org/show_bug.cgi?id=77833

Patch by Priit Laes <plaes@plaes.org> on 2012-02-07
Reviewed by Martin Robinson.

Move checks from webkit.m4 to configure.ac and modernize macros:
  . Check for visibility flags after CXX has been defined
  . Use PKG_PROG_PKG_CONFIG for pkg-config lookup
  . Drop unused LIBFFTW_REQUIRED_VERSION
  . Update ICU libs for mingw (bug 77837).
  . Require Pango 1.21.0 (as per unicode backend)
  . Bump minimum glib version due to g_thread_init changes

* Source/autotools/webkit.m4: Removed.
* configure.ac:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@107016 268f45cc-cd09-0410-ab3c-d52691b4dbfc