build with Meson instead of autotools

So long, autotools!  This is my last MPD related project to migrate
away from it.  It has its strengths, but also very obvious weaknesses
and weirdnesses.  Today, many of its quirks are not needed anymore,
and are cumbersome and slow.  Now welcome our new Meson overlords!

src/CommandLine.cxx

@@ -19,6 +19,7 @@
 
 #include "config.h"
 #include "CommandLine.hxx"
+#include "GitVersion.hxx"
 #include "ls.hxx"
 #include "LogInit.hxx"
 #include "Log.hxx"
@@ -107,11 +108,7 @@ static constexpr Domain cmdline_domain("cmdline");
 gcc_noreturn
 static void version(void)
 {
-	printf("Music Player Daemon " VERSION
-#ifdef GIT_COMMIT
-	       " (" GIT_COMMIT ")"
-#endif
-	       "\n"
+	printf("Music Player Daemon " VERSION " (%s)\n"
 	       "\n"
 	       "Copyright (C) 2003-2007 Warren Dukes <warren.dukes@gmail.com>\n"
 	       "Copyright 2008-2017 Max Kellermann <max.kellermann@gmail.com>\n"
@@ -120,7 +117,8 @@ static void version(void)
 
 #ifdef ENABLE_DATABASE
 	       "\n"
-	       "Database plugins:\n");
+	       "Database plugins:\n",
+	       GIT_VERSION);
 
 	for (auto i = database_plugins; *i != nullptr; ++i)
 		printf(" %s", (*i)->name);