ebuild: pass through android variables

Android exports a bunch of env vars to set the location of source code.
Make sure we pass those down as the 3rd party compiler relies on it.

BUG=24614250
TEST=building packages works w/out errors

Change-Id: Ib0e1741626b9ad25a49ef2c8abf7494e2efc8a27
diff --git a/usr/lib/portage/pym/portage/package/ebuild/config.py b/usr/lib/portage/pym/portage/package/ebuild/config.py
index b75d28c..f3633ed 100644
--- a/usr/lib/portage/pym/portage/package/ebuild/config.py
+++ b/usr/lib/portage/pym/portage/package/ebuild/config.py
@@ -383,6 +383,10 @@
 			env_d = getconfig(os.path.join(eroot, "etc", "profile.env"),
 				tolerant=tolerant, expand=False) or {}
 			expand_map = env_d.copy()
+
+			# Hack in some env vars.
+			# https://bugs.gentoo.org/492854
+			expand_map.update(dict((k, v) for k, v in os.environ.items() if k.startswith('ANDROID_')))
 			self._expand_map = expand_map
 
 			# Allow make.globals to set default paths relative to ${EPREFIX}.