export/helpers: only put helpers in special section for B lang

export/helpers: only put helpers in special section for B lang

B's code generation needs these functions to exist in the object as it
emits some calls to these functions at IR stage, where 'always_inline'
directive results in no symbol for the function being emitted otherwise
as all uses are inlined.

For C, stop putting these helpers in a "helpers" section in object file.
For B, add a `B_WORKAROUND` ifdef check so the "helpers" section is
populated as expected.

There is almost certainly a more elegant way to fix this but would
require digging deep in the b frontend and potentially breaking other
things. Since B frontend hasn't been touched in many years and still
works, let's take the safer but uglier route.