base.bbclass: Add python3-native to native paths for hg fetcher

This helps fix an issue where python interpreter in hg script could
overflow the BINPRM_BUF_SIZE which is 128 on most of systems, because
interpreter is hardcoded and build paths can be deep.

This patch helps, because now the absolute python interp path in hg can
be replaced with '/usr/bin/env python3' and it will ensure that python3
from native install is used instead of the one on host.

(From OE-Core rev: 3adaaab787bd105cc0049d36c7b8caeaa9b633e5)

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Cc: Christopher Larson <chris_larson@mentor.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/base.bbclass

@@ -606,6 +606,7 @@ python () {
         # Mercurial packages should DEPEND on mercurial-native
         elif scheme == "hg":
             needsrcrev = True
+            d.appendVar("EXTRANATIVEPATH", ' python3-native ')
             d.appendVarFlag('do_fetch', 'depends', ' mercurial-native:do_populate_sysroot')
 
         # Perforce packages support SRCREV = "${AUTOREV}"