stop defining _LIBCPP_ENABLE_CXX17_REMOVED_UNEXPECTED_FUNCTIONS when building libc++abi

This was needed because libc++'s <exception> header omits
set_unexpected() (which libcxxabi defines) if that define isn't
set -- but <exception> also doesn't omit it if _LIBCPP_BUILDING_LIBRARY
is defined, which it is after
https://chromium-review.googlesource.com/c/chromium/src/+/3469341

No behavior change.

Bug: 1298070
Change-Id: I6b289656dc9bbc3a5428ac288bda54755bcf221d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3472583
Commit-Queue: Nico Weber <thakis@chromium.org>
Auto-Submit: Nico Weber <thakis@chromium.org>
Reviewed-by: Arthur Eubanks <aeubanks@google.com>
Commit-Queue: Arthur Eubanks <aeubanks@google.com>
Cr-Commit-Position: refs/heads/main@{#972605}
NOKEYCHECK=True
GitOrigin-RevId: 6e3c300d79ea1d1c57fddbf7414c0bb8624c35bc
1 file changed