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.

# This file is part of MXE.
# See index.html for further information.

This patch has been taken from:
http://bugs.gentoo.org/show_bug.cgi?id=305101
http://repos.archlinux.org/wsvn/packages/gd/trunk/libpng14.patch

--- a/gd_png.c
+++ b/gd_png.c
@@ -149,7 +149,7 @@
 	return NULL;
   }
 
-	if (!png_check_sig (sig, 8)) { /* bad signature */
+	if (png_sig_cmp (sig, 0, 8)) { /* bad signature */
     	return NULL;		/* bad signature */
 	}