core: fix windows breakage, r=burningtree.

src/libcore/os.rs

@@ -88,6 +88,10 @@ pub fn fill_charp_buf(f: fn(*mut c_char, size_t) -> bool)
 
 #[cfg(windows)]
 pub mod win32 {
+    use libc;
+    use vec;
+    use str;
+    use option;
     use libc::types::os::arch::extra::DWORD;
 
     pub fn fill_utf16_buf_and_decode(f: fn(*mut u16, DWORD) -> DWORD)

src/libcore/path.rs

@@ -219,6 +219,7 @@ mod stat {
 #[cfg(target_os = "win32")]
 mod stat {
     pub mod arch {
+        use libc;
         pub fn default_stat() -> libc::stat {
             libc::stat {
                 st_dev: 0,