The build API did not catch on outside of Autotools, and Autotools
already conform to that API.

Instead of filling up the build with downstream patches and dealing
with projects breaking the build when moving to Meson, let's stop
pretending other build systems do not exist.

This change requires various modifications that have to land at the
same time in order to avoid breaking the build:

 - we need to modify the wrapper script we use to build each
   component, so that it can detect Meson and invoke it, and
   Ninja, appropriately
 - we need to modify the manifest to drop global configuration
   options that only apply to Autotools, and which will make
   Meson choke
 - we need to turn configuration options we set using the
   Autotools syntax into ones that Meson understands; this also
   means taking default values encoded inside compatibility
   patches