Re-land "Avoid emitting unreachable SP adjustments after `throw`"

This reverts commit 4e0fe038. Re-lands
65b21282.

After landing 5ff5ddd0 to add int3 into
trailing unreachable blocks, we can now remove these extra stack
adjustments without confusing the Win64 unwinder. See
https://llvm.org/45064#c4 or X86AvoidTrailingCall.cpp for a full
explanation.

Fixes PR45064.