Allow changing the link name of extern functions without changing the grammar

[yorickpeterse]

Description

macOS and FreeBSD may include non-standard symbols in function names, such as opendir$INODE64() or fstat@FBSD_1.5 for FreeBSD (see here). Currently we allow dollars in the name so we can handle the former, but we don't handle the case of FreeBSD.

Instead of changing the syntax to allow these special symbols, a better name would be to specify the link name in addition to the call name. A hypothetical syntax would be this:

fn extern opendir as 'opendir$INODE64'(path: Pointer[UInt8]) -> Pointer[UInt8]

Here the as ... bit would specify the name to link the symbol as. The quotes are needed/used so any symbol can be used in the link name. Another option is to flip it around:

fn extern 'opendir$INODE64' as opendir(path: Pointer[UInt8]) -> Pointer[UInt8]

This looks a little less odd, though I'm still not entirely sure about it.

Related work

No response