devtool: show proper error when extracting source for recipes with disabled unpack task

If you try to use "devtool modify -x" or "devtool extract" on a recipe
where do_unpack has been set as noexec (e.g. glibc-locale), then we get
an error because the expected source wasn't ever unpacked. Do a check up
front for noexec being set on do_unpack and error out with a reasonable
message if that's the case.

(From OE-Core rev: 39a93c85e798e72edd6ab3c05f8adbb1a97e893e)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/lib/devtool/standard.py

@@ -261,6 +261,10 @@ def _extract_source(srctree, keep_temp, devbranch, d):
             raise DevtoolError("output path %s already exists and is "
                                "non-empty" % srctree)
 
+    if 'noexec' in (d.getVarFlags('do_unpack', False) or []):
+        raise DevtoolError("The %s recipe has do_unpack disabled, unable to "
+                           "extract source" % pn)
+
     # Prepare for shutil.move later on
     bb.utils.mkdirhier(srctree)
     os.rmdir(srctree)