meson: fix libcl assert() reproducibility

The current -fmacro-prefix-map only handles removal of relative paths
but we still need to handle absolute paths.

The following path can be found in libvulkan_panfrost.so when building
with Yocto for example:
/work/build/tmp/work/cortexa76-cortexa55-crypto-poky-linux/mesa/25.2.0/sources/mesa-25.2.0/src/panfrost/libpan/../../util/bitpack_helpers.h

These paths currently seem to only appear in the binary in strings that
start with "Shader assertion fail at " which seems to indicate there are
calls to assert() with absolute paths as well as relative paths (which
are already patched with fmacro-prefix-map).

By stripping the project source and build root directories from the
paths with -fmacro-prefix-map, we get rid of this reproducibility issue
(which incidentally makes the build fail due to buildpaths QA issue).

Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36927>
(cherry picked from commit b1a28b1165)

.pick_status.json

@@ -4164,7 +4164,7 @@
         "description": "meson: fix libcl assert() reproducibility",
         "nominated": false,
         "nomination_type": 0,
-        "resolution": 4,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": null,
         "notes": null

meson.build

@@ -52,6 +52,8 @@ relative_dir = fs.relative_to(meson.project_source_root(), meson.project_build_r
 
 cl_args = [
   '-fmacro-prefix-map=@0@/='.format(relative_dir),
+  '-fmacro-prefix-map=@0@/='.format(meson.project_source_root()),
+  '-fmacro-prefix-map=@0@/='.format(meson.project_build_root()),
 
   # Set the OpenCL standard to CL 2.0, enabling everything at a frontend.
   # Drivers may not actually support everything but that's ok.