m4: grab newer upstream m4 (for code-coverage)

Grab some newer version of the autotools m4 archive, as we need those to
setup code-coverage.

Remove some unneeded ones.

m4/Makefile.am

@@ -1,4 +1,4 @@
-## Copyright (C) 2008-2017 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
+## Copyright (C) 2008-2020 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
 ##
 ## This program is free software; you can redistribute it and/or modify
 ## it under the terms of the GNU General Public License as published by
@@ -16,12 +16,28 @@
 
 include $(top_srcdir)/gtest.mk
 
-EXTRA_DIST =				\
-	ax_cxx_compile_stdcxx.m4	\
+EXTRA_DIST=				\
+	ax_ac_append_to_file.m4		\
+	ax_ac_print_to_file.m4		\
+	ax_add_am_macro_static.m4	\
+	ax_am_macros_static.m4		\
+	ax_append_compile_flags.m4	\
+	ax_append_flag.m4		\
+	ax_append_link_flags.m4		\
+	ax_check_compile_flag.m4	\
+	ax_check_enable_debug.m4	\
+	ax_check_gnu_make.m4		\
+	ax_check_link_flag.m4		\
+	ax_code_coverage.m4		\
+	ax_compiler_flags_cflags.m4	\
+	ax_compiler_flags_cxxflags.m4	\
+	ax_compiler_flags_gir.m4	\
+	ax_compiler_flags_ldflags.m4	\
+	ax_compiler_flags.m4		\
 	ax_cxx_compile_stdcxx_14.m4	\
+	ax_cxx_compile_stdcxx.m4	\
+	ax_file_escapes.m4		\
+	ax_is_release.m4		\
+	ax_require_defined.m4		\
 	ax_valgrind_check.m4		\
-	guile.m4			\
-	lib-ld.m4			\
-	lib-link.m4			\
-	lib-prefix.m4			\
-	perlmod.m4
+	guile-2.2.m4