nettle: Respect portage host cc variable

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

Gentoo PR: https://github.com/gentoo/gentoo/pull/16156

BUG=chromium:979916, chromium:991812, chromium:1088242
TEST=CQ

Change-Id: I8cc38fb3cb8094d5e9ef0aad35e3755b7ab1e09d
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/portage-stable/+/2240124
Tested-by: Manoj Gupta <manojgupta@chromium.org>
Reviewed-by: George Burgess <gbiv@chromium.org>
1 file changed