Revert r185872 - "Stop emitting weak symbols into the "coal" sections"

This patch broke `make check-asan` on Mac, causing ld warnings like the following one:

ld: warning: direct access in __GLOBAL__I_a to global weak symbol
___asan_mapping_scale means the weak symbol cannot be overridden at
runtime. This was likely caused by different translation units being
compiled with different visibility settings.

The resulting test binaries crashed with incorrect ASan warnings.
[PowerPC] Support ".machine any"

The PowerPC assembler is supposed to provide a directive .machine
that allows switching the supported CPU instruction set on the fly.
Since we do not yet check CPU feature sets at all and always accept
any available instruction, this is not really useful at this point.

However, it makes sense to accept (and ignore) ".machine any" to
avoid spuriously rejecting existing assembler files that use this.