[lld] [ELF] Support DW_EH_PE_sdata8 encoding in .eh_frame_hdr (PR #179089)

[via llvm-commits]

PiJoules wrote:

👋  It looks like this leads to a segfault when linking some fuchsia binaries with CFI + thinlto

```
Process 300674 launched: '/usr/local/google/home/leonardchan/llvm-projects/llvm-project-build-1/bin/ld.lld' (x86_64)
Process 300674 stopped
* thread #1, name = 'ld.lld', stop reason = signal SIGSEGV: address not mapped to object (fault address=0x68)
    frame #0: 0x00005555595adf50 ld.lld`lld::elf::EhFrameHeader::updateAllocSize(this=0x0000555563ba7570, ctx=0x0000555563a189e0) at SyntheticSections.cpp:621:46
Likely cause: lld::elf::InputSection::getParent() const()->addr accessed 0x68
(lldb) bt
* thread #1, name = 'ld.lld', stop reason = signal SIGSEGV: address not mapped to object (fault address=0x68)
  * frame #0: 0x00005555595adf50 ld.lld`lld::elf::EhFrameHeader::updateAllocSize(this=0x0000555563ba7570, ctx=0x0000555563a189e0) at SyntheticSections.cpp:621:46
    frame #1: 0x00005555596b3944 ld.lld`(anonymous namespace)::Writer<llvm::object::ELFType<(llvm::endianness)1, true>>::finalizeAddressDependentContent(this=0x00007fffffffb030) at Writer.cpp:1607:37
    frame #2: 0x00005555596ae640 ld.lld`(anonymous namespace)::Writer<llvm::object::ELFType<(llvm::endianness)1, true>>::finalizeSections(this=0x00007fffffffb030) at Writer.cpp:2159:3
    frame #3: 0x000055555968695f ld.lld`(anonymous namespace)::Writer<llvm::object::ELFType<(llvm::endianness)1, true>>::run(this=0x00007fffffffb030) at Writer.cpp:323:3
    frame #4: 0x00005555596c690b ld.lld`void lld::elf::writeResult<llvm::object::ELFType<(llvm::endianness)1, true>>(ctx=0x0000555563a189e0) at Writer.cpp:100:21
    frame #5: 0x00005555593866ac ld.lld`void lld::elf::LinkerDriver::link<llvm::object::ELFType<(llvm::endianness)1, true>>(this=0x0000555563a191f0, args=0x00007fffffffbc68) at Driver.cpp:3514:3
    frame #6: 0x0000555559360cab ld.lld`lld::elf::LinkerDriver::linkerMain(this=0x0000555563a191f0, argsArr=ArrayRef<const char *> @ 0x00007fffffffbeb0) at Driver.cpp:731:16
    frame #7: 0x000055555936052d ld.lld`lld::elf::link(args=ArrayRef<const char *> @ 0x00007fffffffc130, stdoutOS=0x0000555563974d30, stderrOS=0x0000555563974db0, exitEarly=true, disableOutput=false) at Driver.cpp:140:14
    frame #8: 0x00005555591c7d70 ld.lld`lld::unsafeLldMain(args=ArrayRef<const char *> @ 0x00007fffffffc9e0, stdoutOS=0x0000555563974d30, stderrOS=0x0000555563974db0, drivers=ArrayRef<lld::DriverDef> @ 0x00007fffffffc9d0, exitEarly=true) at DriverDispatcher.cpp:163:12
    frame #9: 0x0000555558cc4730 ld.lld`lld_main(argc=2, argv=0x00007fffffffd7b8, (null)=0x00007fffffffd040) at lld.cpp:90:9
    frame #10: 0x00005555591c72cc ld.lld`findTool(Argc=2, Argv=0x00007fffffffd7b8, Argv0="/usr/local/google/home/leonardchan/llvm-projects/llvm-project-build-1/bin/ld.lld") at LLVMDriverTools.def:32:1
    frame #11: 0x00005555591c6265 ld.lld`main(Argc=2, Argv=0x00007fffffffd7b8) at llvm-driver.cpp:85:10
    frame #12: 0x00007ffff7cd8ca8 libc.so.6`__libc_start_call_main(main=(ld.lld`main at llvm-driver.cpp:83), argc=2, argv=0x00007fffffffd7b8) at libc_start_call_main.h:58:16
    frame #13: 0x00007ffff7cd8d65 libc.so.6`__libc_start_main_impl(main=(ld.lld`main at llvm-driver.cpp:83), argc=2, argv=0x00007fffffffd7b8, init=<unavailable>, fini=<unavailable>, rtld_fini=<unavailable>, stack_end=0x00007fffffffd7a8) at libc-start.c:360:3
    frame #14: 0x0000555558ca5f29 ld.lld`_start + 41
```

Not yet sure if this is us holding anything incorrectly or if it's a direct result of this patch, but we do know this was linking prior to this change.

Github won't let me attach tar files so here's a google drive link to it: https://drive.google.com/file/d/1zZfCLZx9MWCrD9mbUCMMl767SIRqSF8d/view?usp=sharing

https://github.com/llvm/llvm-project/pull/179089