-C panic=abort doesn't generate EHABI information on arm

[makotokato]

From https://bugzilla.mozilla.org/show_bug.cgi?id=1453220

Gecko profiler uses EHABI information to walk stack. But since rustc doesn't generate EHABI, it cannot walk stack on generated code by rust.

@glandium says, "-C panic=abort" causes that EHABI isn't emitted", so we need a option not to remove it (or don't remove EHABI even if -C panic=abort).

[glandium]

Note the same actually applies to EH_FRAME info on x86-64, which iirc the Firefox profiler also uses on x86-64. More generally, it can be desirable to have unwind info even when panic doesn't unwind.

[luser]

For C/C++ code in Firefox we use -funwind-tables to ensure that the compiler generates these when --enable-profiling is on:
https://dxr.mozilla.org/mozilla-central/rev/0a2dae2d8cf9f628c55668514c54a23da446d5de/build/autoconf/frameptr.m4#12

The equivalent for x86-64 is -fasynchronous-unwind-tables which is apparently on by default.

It seems like having a compiler option to enable this would be good enough, since the behavior here mirrors what gcc does: only emit unwind info if needed for exceptions/unwinding.

[makotokato]

LLVM seems to turn on EHABI as default by https://reviews.llvm.org/D2627 (EnableARMEHABI is removed by this landing, but src/rustllvm/PassWrapper.cpp still has it)
#40549 is similar issue for Win64 ABI.

[alexcrichton]

This may or may not be related to #45031, but I can prepare a patch like #40549 for the targets here. @makotokato do you know what targets are in use by Firefox and would need this treatment?