meson: Fix build from tarball

Include xml2-config-meson in EXTRA_DIST.

Fixes #883.

Author: nwellnhof

Makefile.am

@@ -215,7 +215,7 @@ EXTRA_DIST = Copyright libxml2-config.cmake.in autogen.sh \
 	     timsort.h \
 	     README.zOS README.md \
 	     CMakeLists.txt config.h.cmake.in libxml2-config.cmake.cmake.in \
-	     meson.build meson_options.txt
+	     meson.build meson_options.txt xml2-config-meson
 
 
 pkgconfigdir = $(libdir)/pkgconfig