Add new syntax extension fourcc!()

fourcc!() allows you to embed FourCC (or OSType) values that are
evaluated as u32 literals. It takes a 4-byte ASCII string and produces
the u32 resulting in interpreting those 4 bytes as a u32, using either
the platform-native endianness, or explicitly as big or little endian.

src/libsyntax/ext/base.rs

@@ -194,6 +194,9 @@ pub fn syntax_expander_table() -> SyntaxEnv {
     syntax_expanders.insert(intern("bytes"),
                             builtin_normal_expander(
                                     ext::bytes::expand_syntax_ext));
+    syntax_expanders.insert(intern("fourcc"),
+                            builtin_normal_tt_no_ctxt(
+                                    ext::fourcc::expand_syntax_ext));
     syntax_expanders.insert(intern("concat_idents"),
                             builtin_normal_expander(
                                     ext::concat_idents::expand_syntax_ext));