Drop mingw-w64 gcc toolchain ported from fedora

Using the one directly provided by Archlinux community.
win-iconv: using mingw-w64-cmake

Instead of hardcode the CMake scripts in the package, use the one
provided by AUR.
zlib: follow MinGW PKGBUILD guidelines
bzip2: follow MinGW PKGBUILD guidelines
expat: follow MinGW PKGBUILD guidelines
termcap: follow MinGW PKGBUILD guidelines
libxml2: follow MinGW PKGBUILD guidelines
libpng: follow MinGW PKGBUILD guidelines
libjpeg-turbo: follow MinGW PKGBUILD guidelines
libffi: follow MinGW PKGBUILD guidelines
glib2: follow MinGW PKGBUILD guidelines
doc: include mingw-w64-tools in dependencies

That package is required for building cairo in two stages. Until this
two step process is not resolved, the dependency should be kept.
nsis: rename fedora-nsis to fedora-mingw-w64-nsis

Be more consistent with the naming convention of the other packages.
atk: follow MinGW PKGBUILD guidelines
cairo: follow MinGW PKGBUILD guidelines
fontconfig: follow MinGW PKGBUILD guidelines
freetype: follow MinGW PKGBUILD guidelines
gdk-pixbuf: follow MinGW PKGBUILD guidelines
gtk2: follow MinGW PKGBUILD guidelines
gtk3: follow MinGW PKGBUILD guidelines