Add NetBSD support

Mostly picking the same paths as FreeBSD.
We need a little special handling for crt files, as netbsd uses its
own (and not GCC's) for those, with slightly different names.

src/target.cpp

@@ -743,6 +743,7 @@ uint32_t target_c_type_size_in_bits(const ZigTarget *target, CIntType id) {
         case OsMacOSX:
         case OsZen:
         case OsFreeBSD:
+	case OsNetBSD:
         case OsOpenBSD:
             switch (id) {
                 case CIntTypeShort:
@@ -783,7 +784,6 @@ uint32_t target_c_type_size_in_bits(const ZigTarget *target, CIntType id) {
         case OsIOS:
         case OsKFreeBSD:
         case OsLv2:
-        case OsNetBSD:
         case OsSolaris:
         case OsHaiku:
         case OsMinix: