The default is to enable (and autodetect based on lscpu) simd support,
or the mode can be specified via --enable-simd=mode. --disable-simd
disables the support but ensures gcc will still compile the float vector
types.
QF_PROCESS_NEED_LIST is a better name as for one, building no longer
depends on directories, and the directories were lists anyway, so the
name is more generally applicable.
Most of the guts of configure.ac have been moved to config.d and are then
brought in by m4_include. This will make maintaining configure.ac much easier.
Also drop use of PROGRAM and VERSION, using PACKAGE_NAME, PACKAGE_VERSION, and
on occasion, PACKAGE_STRING instead, and clean out some old files we no longer
need.
