Make SYSROOT a portage variable

SYSROOT should be a special variable and not get included in the binary
package's environment.

BUG=chromium:404018
TEST=inspect environment.bz2 from a binary package. SYSROOT is not defined
there.
TEST=trybot run on daisy, duck, link, gizmo, mispel32, chromiumos-sdk.

Change-Id: I2b93bd37dda2263e7ccb2ccf9e7f9963a4fa5bc7
Reviewed-on: https://chromium-review.googlesource.com/221343
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Bertrand Simonnet <bsimonnet@chromium.org>
diff --git a/bin/save-ebuild-env.sh b/bin/save-ebuild-env.sh
index 98cff83..3702afa 100644
--- a/bin/save-ebuild-env.sh
+++ b/bin/save-ebuild-env.sh
@@ -106,7 +106,7 @@
 		PORTAGE_SANDBOX_READ PORTAGE_SANDBOX_WRITE PREROOTPATH \
 		QA_INTERCEPTORS \
 		RC_DEFAULT_INDENT RC_DOT_PATTERN RC_ENDCOL RC_INDENTATION  \
-		ROOT ROOTPATH RPMDIR TEMP TMP TMPDIR USE_EXPAND \
+		ROOT ROOTPATH RPMDIR SYSROOT TEMP TMP TMPDIR USE_EXPAND \
 		WARN XARGS _RC_GET_KV_CACHE
 
 	# user config variables
diff --git a/pym/portage/package/ebuild/_config/special_env_vars.py b/pym/portage/package/ebuild/_config/special_env_vars.py
index 74fedd6..06f3484 100644
--- a/pym/portage/package/ebuild/_config/special_env_vars.py
+++ b/pym/portage/package/ebuild/_config/special_env_vars.py
@@ -76,7 +76,7 @@
 	"PORTAGE_VERBOSE", "PORTAGE_WORKDIR_MODE", "PORTAGE_XATTR_EXCLUDE",
 	"PORTDIR", "PORTDIR_OVERLAY", "PREROOTPATH", "PROFILE_PATHS",
 	"REPLACING_VERSIONS", "REPLACED_BY_VERSION",
-	"ROOT", "ROOTPATH", "T", "TMP", "TMPDIR",
+	"ROOT", "ROOTPATH", "SYSROOT", "T", "TMP", "TMPDIR",
 	"USE_EXPAND", "USE_ORDER", "WORKDIR",
 	"XARGS", "__PORTAGE_TEST_HARDLINK_LOCKS",
 ]