protobuf: Respect portage host cc variable

Pass CC_FOR_BUILD and CXX_FOR_BUILD to econf.
Otherwise it invokes gcc/g++ instead of portage specified HOST/BUILD CC.

Gentoo PR: https://github.com/gentoo/gentoo/pull/16181

BUG=chromium:979916, chromium:991812, chromium:1093633
TEST=CQ

Change-Id: I538d2be016a3935cf66e74c2511ecdb880759f6b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/portage-stable/+/2238521
Tested-by: Manoj Gupta <manojgupta@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Manoj Gupta <manojgupta@chromium.org>
diff --git a/dev-libs/protobuf/protobuf-3.11.4.ebuild b/dev-libs/protobuf/protobuf-3.11.4-r1.ebuild
similarity index 97%
rename from dev-libs/protobuf/protobuf-3.11.4.ebuild
rename to dev-libs/protobuf/protobuf-3.11.4-r1.ebuild
index 5cf6489..ad57030 100644
--- a/dev-libs/protobuf/protobuf-3.11.4.ebuild
+++ b/dev-libs/protobuf/protobuf-3.11.4-r1.ebuild
@@ -58,6 +58,8 @@
 
 multilib_src_configure() {
 	local options=(
+		CC_FOR_BUILD="$(tc-getBUILD_CC)"
+		CXX_FOR_BUILD="$(tc-getBUILD_CXX)"
 		$(use_enable static-libs static)
 		$(use_with zlib)
 	)