meson: implement split-debug

split-debug uses C args `--gsplit-dwarf` and linker args `--gdb-index`
to achieve split debug, speed up the CI linking, and allow us to
distribute debug symbols standalone.

Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
Signed-off-by: David Heidelberg <david.heidelberg@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28576>

meson_options.txt

@@ -1,6 +1,12 @@
 # Copyright © 2017-2019 Intel Corporation
 # SPDX-License-Identifier: MIT
 
+option(
+  'split-debug',
+  type : 'feature',
+  value : 'disabled',
+  description : 'split debug information (-gsplit-dwarf compile flag) and debug information in the gdb index format (--gdb-index)',
+)
 option(
   'platforms',
   type : 'array',