cros-i686, cros-arm64: Remove unneeded workarounds

Use libc++ and drop workarounds for building 32-bit x86 and
64-bit arm64 static binaries.
Changed "-isystem" to "-idirafter" for <board>/usr/include so that is
used at end rather than beginning and avoids confusing clang because of
headers of a different ABI. "-idirafter" directory is still treated as
a system include directory.

BUG=chromium:991024, chromium:1158137
TEST=CQ

Change-Id: I6cb81c0e5859586b1f46a5a7fd711deb5de002ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/2586271
Tested-by: Manoj Gupta <manojgupta@chromium.org>
Commit-Queue: Manoj Gupta <manojgupta@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Auto-Submit: Manoj Gupta <manojgupta@chromium.org>
4 files changed