[libunwind] Make sure libunwind test dependencies are installed before running tests (#171474)
This patch adds an installation step where we install libc++ in a fake
installation tree before testing libunwind. This is necessary because
some configurations (in particular "generic-merged") require libc++ to
be installed, since the libunwind tests are actually linking libc++.so
in which libc++abi.a and libunwind.a have been merged.
Without this, we were actually failing to find `libc++.so` to link
against and then linking against whatever system library we'd find in
the provided search directories. While this happens to work in the
current CI configuration, this breaks down when updating to newer build
tools.
NOKEYCHECK=True
GitOrigin-RevId: fb8a7c774d62406bba98765236111159edfa96c1
2 files changed
