add uninitialized machine system and default to it.

Prior to this dragonfly bsd happened to be the default system which was
pretty confusing when trying to use build/host machine before it was
initialized.

include/machines.h

@@ -12,6 +12,8 @@
 #include "platform/uname.h"
 
 enum machine_system {
+	machine_system_uninitialized = 0,
+	machine_system_unknown = 1,
 	machine_system_dragonfly,
 	machine_system_freebsd,
 	machine_system_gnu,
@@ -26,7 +28,6 @@ enum machine_system {
 	machine_system_cygwin,
 	machine_system_msys2,
 	machine_system_darwin,
-	machine_system_unknown,
 };
 
 enum machine_kind {

src/machines.c

@@ -67,6 +67,8 @@ const char *
 machine_system_to_s(enum machine_system sys)
 {
 	switch (sys) {
+	case machine_system_uninitialized: return "<uninitialized>";
+	case machine_system_unknown: return "unknown";
 	case machine_system_dragonfly: return "dragonfly";
 	case machine_system_freebsd: return "freebsd";
 	case machine_system_gnu: return "gnu";
@@ -81,7 +83,6 @@ machine_system_to_s(enum machine_system sys)
 	case machine_system_cygwin: return "cygwin";
 	case machine_system_msys2: return "msys2";
 	case machine_system_darwin: return "darwin";
-	case machine_system_unknown: return "unknown";
 	}
 
 	UNREACHABLE_RETURN;