uninative.bbclass: handle read only files outside of patchelf

We are seeing autobuilder failures with the latest uninative:

patchelf: open: Permission denied

See upstream discussion which suggests handling
read-only files explicitly outside of patchelf:
https://github.com/NixOS/patchelf/pull/89

(From OE-Core rev: 3680fcbf9ba327aedb32bb4eb647dd56fcccfd51)

Signed-off-by: Steve Sakoman <steve@sakoman.com>

meta/classes/uninative.bbclass

@@ -169,5 +169,7 @@ python uninative_changeinterp () {
             if not elf.isDynamic():
                 continue
 
+            os.chmod(f, s[stat.ST_MODE] | stat.S_IWUSR)
             subprocess.check_output(("patchelf-uninative", "--set-interpreter", d.getVar("UNINATIVE_LOADER"), f), stderr=subprocess.STDOUT)
+            os.chmod(f, s[stat.ST_MODE])
 }