Update mesa to version 20.0.8 (bug #58689). * src/mesa.mk: Update version and checksum. Add build-meson to dependecies. Update build rule to use meson and ninja as the build tools. * src/mesa-1-meson.patch: Add new patch. * src/mesa-1-fixes.patch: Remove old patch for the scons rule that is no longer needed. * dist-files.mk: Update file list. * src/build-mako.mk: Depend on and use python3. * src/build-markupsafe.mk: Depend on and use python3.

Don't link to Win32 library libstdc++

diff --git "a/meson.build" "b/meson.build"
index eaaca7f..9b9d2d3 100644
--- "a/meson.build"	
+++ "b/meson.build"
@@ -1030,8 +1030,7 @@ if host_machine.system() == 'windows'
     add_project_link_arguments(
       '-Wl,--nxcompat',
       '-Wl,--dynamicbase',
       '-static-libgcc',
-      '-static-libstdc++',
       language : ['c', 'cpp'],
     )
   endif