ncurses: upgraded package to upstream

Upgraded sys-libs/ncurses to version 6.2-r1 on amd64

COS specific changes:
 - Added custom patches for "LD" (ncurses-6.2-prefix-ld.patch) and "PKG_CONFIG" (ncurses-6.2-pkgconfig-prefix.patch) so that build uses prefixed tools.
 - Set CC=${BUILD_CC}

Upstream patch for `CC` change: https://github.com/gentoo/gentoo/pull/21984

BUG=b/196649228,b/196648873
TEST=presubmit
RELEASE_NOTE=Upgraded sys-libs/ncurses to version 6.2-r1. This resolves CVE-2019-17594 and CVE-2019-17595.

Change-Id: Id145152b77bb1902cfd13dd45960d756a1a3e0d6
Reviewed-on: https://cos-review.googlesource.com/c/third_party/overlays/portage-stable/+/12533
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
19 files changed