pgo: replace meson-pgo.sh with several script primitives

All scripts are in the ‘pgo’ directory:

* options: command line options for generate-alt-random-writes.py,
  sourced by other scripts.

* pgo.sh: top-level script, generates a meson build directory, selects
  a PGO method, generates the profiling data, re-configures the meson
  build directory and does the final build.

  This script is intended to be used by end-users, and shows _how_ to
  integrate the script primitives.

  Build servers will most likely *not* want to use this script as-is.

* partial.sh: generates alt-random-write data and runs “foot{,client}
  --version”, and then feeds the alt-random data to the PGO helper
  binary. Does not require a running Wayland session. Touches
  $blddir/pgo-ok on success.

* full-inner.sh: runs “footclient --version”, and then a complex
  “foot” command that first generates alt-random-write data, and then
  “cat’s” it. Requires a running Wayland session, *but*, this script
  is usually not called directly (see below). Touches $blddir/pgo-ok
  onsucces..

* full-current-session.sh: runs full-inner.sh. That is, it runs foot
  in the currently running Wayland session. Note that this will pop up a
  foot window.

* full-headless-sway.sh: generates a custom Sway configuration that
  exec’s foot-headless-sway-inner.sh (see below), and then executes a
  headless Sway. In other words, this script does a *full* PGO build,
  but *without* requiring a running Wayland session. Requires Sway >=
  1.6.2.

* full-headless-sway.sh: runs full-inner.sh + “swaymsg exit”.

To do a custom PGO build, without using pgo.sh, you’d need to:

CFLAGS=”$CFLAGS -O3” meson --buildtype=release -Db_lto=true
meson configure -Db_pgo=generate
ninja
ninja test (only needed if tllist+fcft are built as subprojects)

Run *one* of:
  - partial.sh
  - full-current-session.sh
  - full-headless-sway.sh

meson configure -D b_pgo=use
ninja

pgo/options

@@ -0,0 +1 @@
+script_options="--scroll --scroll-region --colors-regular --colors-bright --colors-256 --colors-rgb --attr-bold --attr-italic --attr-underline --sixel"