build: Port to meson

meson is a build system focused on speed an ease of use, which
helps speeding up the software development. This patch adds meson
support along autotools.

include/meson.build

@@ -0,0 +1,41 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+# Copyright (C) 2021 Iñigo Martinez <inigomartinez@gmail.com>
+
+include_inc = include_directories('.')
+
+mm_enums_header = files('ModemManager-enums.h')
+mm_errors_header = files('ModemManager-errors.h')
+
+headers = files(
+  'ModemManager-compat.h',
+  'ModemManager.h',
+)
+
+install_headers(
+  headers + mm_enums_header + mm_errors_header,
+  install_dir: mm_pkgincludedir,
+)
+
+header = 'ModemManager-names.h'
+
+mm_names_header = custom_target(
+  header,
+  input: [build_aux_dir / 'header-generator.xsl', mm_ifaces_all],
+  output: header,
+  command: [find_program('xsltproc'), '--xinclude', '--nonet', '--output', '@OUTPUT@', '@INPUT@'],
+  install: true,
+  install_dir: mm_pkgincludedir,
+)
+
+mm_version_header = configure_file(
+  input: 'ModemManager-version.h.in',
+  output: '@BASENAME@',
+  configuration: version_conf,
+  install: true,
+  install_dir: mm_pkgincludedir,
+)
+
+include_dep = declare_dependency(
+  sources: [mm_names_header, mm_version_header],
+  include_directories: include_inc,
+)