update blksize_t in raw to reflect libc change under openbsd

Author: semarie

src/libstd/os/openbsd/raw.rs

@@ -16,7 +16,7 @@ use os::raw::c_long;
 use os::unix::raw::{uid_t, gid_t};
 
 #[stable(feature = "raw_ext", since = "1.1.0")] pub type blkcnt_t = i64;
-#[stable(feature = "raw_ext", since = "1.1.0")] pub type blksize_t = u32;
+#[stable(feature = "raw_ext", since = "1.1.0")] pub type blksize_t = i32;
 #[stable(feature = "raw_ext", since = "1.1.0")] pub type dev_t = i32;
 #[stable(feature = "raw_ext", since = "1.1.0")] pub type fflags_t = u32;
 #[stable(feature = "raw_ext", since = "1.1.0")] pub type ino_t = u64;