[lld/mac] Make binaries written by lld strippable
Be less clever when writing the indirect symbols in LC_DYSYMTAB:
lld used to make point stubs and la_symbol_ptr point at the
same bytes in the indirect symbol table in the LINKEDIT segment.
That confused strip, so write the same bytes twice and make
stubs and __la_symbol_ptr point at one copy each, so that they
don't share data. This unconfuses strip, and seems to be what ld64
does too, so hopefully tools are generally more used to this.
This makes the output binaries a bit larger, but not much: 4 bytes
for roughly each called function from a dylib and each weak function.
Chromium Framewoork grows by 6536 bytes, clang-format by a few hundred.
With this, strip -x Chromium\ Framework works (244 MB before stripping
to 171 MB after stripping, compared to 236 MB=>164 MB with ld64). Running
strip without -x produces the same error message now for lld-linked
Chromium Framework as for when using ld64 as a linker.
strip clang-format also works now but didn't previously.
Differential Revision: https://reviews.llvm.org/D104081