cairo, harfbuzz: rework atomic dependencies

cairo, harfbuzz: rework atomic dependencies

This commit handles the reverse dependency tree of cairo in terms of
atomic dependencies. There are two main changes:

 - cairo in fact no longer needs atomic operations. It can perfectly
   build without any __sync built-in, as was tested using an ARC
   toolchain without atomics, and a SPARC toolchain. Optionally, Cairo
   can use the __atomic builtins provided by gcc >= 4.7, so support
   for this is added as well. Thanks to this change, the
   BR2_ARCH_HAS_ATOMICS dependency is removed from cairo and all its
   reverse dependencies.

 - harfbuzz does require the __sync built-in for 4 bytes integers, so
   we add a dependency on BR2_TOOLCHAIN_HAS_SYNC_4 to harfbuzz and all
   its reverse dependency, the main one being the pango package. Due
   to this, the vast majority of gtk-related packages are moved to a
   dependency on BR2_ARCH_HAS_ATOMICS (which used to be due to cairo)
   to a dependency on BR2_TOOLCHAIN_HAS_SYNC_4 (due to pango ->
   harfbuzz).

In detail:

 - cairo

   Remove BR2_ARCH_HAS_ATOMICS dependency, link against -latomic when
   gcc >= 4.8 in order to use the __atomic functions.

 - harfbuzz

   Add dependency on BR2_TOOLCHAIN_HAS_SYNC_4

 - cairomm, gst-plugins-good, gst1-plugins-good, libgdiplus,
   libsvg-cairo, weston

   Remove BR2_ARCH_HAS_ATOMICS dependency (since cairo no longer needs
   atomics)

 - enlightenment, cwiid, gst-plugins-bad, gst-plugins-base,
   gst1-plugins-bad, gst1-plugins-base, gtkmm3,
   libevas-generic-loaders, libfm, libgail, libgtk2, libgtk3, librsvg,
   openbox, opencv, opencv3, pango, pangomm, pcmanfm, pinentry,
   rrdtool, webkit, webkitgtk24, xscreensaver

   Switch from a BR2_ARCH_HAS_ATOMICS dependency to a
   BR2_TOOLCHAIN_HAS_SYNC_4 (they depend on pango, harfbuzz, gtk, or
   some other related package)

 - directfb

   Remove BR2_ARCH_ATOMICS dependency of the BR2_PACKAGE_DIRECTFB_SVG
   (since cairo can build without atomics), but add a
   BR2_TOOLCHAIN_HAS_SYNC_4 dependency on BR2_PACKAGE_DIRECTFB itself
   since it does use __sync built-ins. This replaces the !BR2_sparc
   dependency.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>