Add fallocate64 and posix_fallocate64 bindings

These are necessary for large file support on 32-bit platforms,
following the same pattern as 74825222 ("Add bindings for
-D_FILE_OFFSET_BITS=64").

Signed-off-by: Daniel Verkamp <dverkamp@chromium.org>

src/unix/notbsd/linux/mod.rs

@@ -1816,8 +1816,12 @@ extern {
     pub fn ftello64(stream: *mut ::FILE) -> ::off64_t;
     pub fn fallocate(fd: ::c_int, mode: ::c_int,
                      offset: ::off_t, len: ::off_t) -> ::c_int;
+    pub fn fallocate64(fd: ::c_int, mode: ::c_int,
+                       offset: ::off64_t, len: ::off64_t) -> ::c_int;
     pub fn posix_fallocate(fd: ::c_int, offset: ::off_t,
                            len: ::off_t) -> ::c_int;
+    pub fn posix_fallocate64(fd: ::c_int, offset: ::off64_t,
+                             len: ::off64_t) -> ::c_int;
     pub fn readahead(fd: ::c_int, offset: ::off64_t,
                      count: ::size_t) -> ::ssize_t;
     pub fn getxattr(path: *const c_char, name: *const c_char,