meson: update to 0.50.0

meson: update to 0.50.0

Remove 0001-Linker-rules-move-cross_args-in-front-of-output_args.patch
as the upstream code has been completely reworked; if the issues pops up
again, we need to re-write the fix.

Rebase:
0001-Make-CPU-family-warnings-fatal.patch
0001-environment.py-detect-windows-also-if-the-system-str.patch
0001-gtkdoc-fix-issues-that-arise-when-cross-compiling.patch
0002-Support-building-allarch-recipes-again.patch

Add 0001-mesonbuild-environment.py-check-environment-for-vari.patch
as particularly we set windows resource compiler through an
environment variable WINDRES. This has replaced the
0001-modules-windows-split-WINDRES-env-variable.patch as the code
has been refactored.

Add 0001-mesonbuild-environment.py-do-not-determine-whether-a.patch
for a more robust detection of cross builds.

Replace many-cross.patch with corresponding backports from upcoming 0.50.1:
0007-mesonbuild-allow-multiple-cross-file-options.patch
load-configs-generalise-search-path.patch

Drop cross-libdir.patch as it has been merged upstream.

Signed-off-by: Alexander Kanavin <alex.kanavin@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>