Auto merge of #91654 - nikic:llvmbc-section-flags, r=nagisa

Auto merge of #91654 - nikic:llvmbc-section-flags, r=nagisa

Use module inline assembly to embed bitcode

In LLVM 14, our current method of setting section flags to avoid
embedding the `.llvmbc` section into final compilation artifacts
will no longer work, see issue #90326. The upstream recommendation
is to instead embed the entire bitcode using module-level inline
assembly, which is what this change does.

I've kept the existing code for platforms where we do not need to
set section flags, but possibly we should always be using the
inline asm approach (which would have to look a bit different for MachO).

r? `@nagisa`