this allows a compiler derivation to provide a
hardeningUnsupportedFlagsByTargetPlatform passthru attr
that will be called with the targetPlatform to determine
the unsupported hardening flags for that platform.
we can do this because even though a clang compiler is
multi-target by nature, cc-wrapper effectively fixes the
target platform at wrapping time. otherwise we'd have to
sniff the intended target at runtime, which wouldn't
be fun at all.
the advantage of using a new attribute instead of
allowing hardeningUnsupportedFlags to optionally be a
function is that hardeningUnsupportedFlags retains its
simple overriding pattern for simple cases (i.e.
`(prev.hardeningUnsupportedFlags or []) ++ [ "foo" ]`
) which will continue to work as long as the bottom-most
function of hardeningUnsupportedFlagsByTargetPlatform
falls back to hardeningUnsupportedFlags.
c33c7c3d5f ("clang_11: Fix RISC-V builds for compiler-rt. (#135718)")
already marked tihs as broken for LLVM 11, but didn't apply the same
change to other affected LLVM versions.
This change applies the upstream PR
https://github.com/llvm/llvm-project/pull/77218 so the same link flags
on darwin are used as when LIBCXX_CXX_ABI=libcxxabi. Specifically, this
adds
"-Wl,-force_symbols_not_weak_list,${CMAKE_CURRENT_SOURCE_DIR}/../lib/notweak.exp"
which prevents libcxx from segfaulting on darwin
compiler-rt includes <linux/unistd.h> on RISC-V. This only seems to
be necessary for useLLVM, but looking at the source code I can't
see any reason for that, so probably in the non-useLLVM case it just
gets propagated in.
