Add a compilation section to disable address maps

[alexcrichton]

This commit adds a new Config::generate_address_map compilation
setting which is used to disable emission of the .wasmtime.addrmap
section of compiled artifacts. This section is currently around the size
of the entire .text section itself unfortunately and for size reasons
may wish to be omitted. Functionality-wise all that is lost is knowing
the precise wasm module offset address of a faulting instruction or in a
backtrace of instructions. This also means that if the module has DWARF
debugging information available with it Wasmtime isn't able to produce a
filename and line number in the backtrace.

This option remains enabled by default. This option may not be needed in
the future with #3547 perhaps, but in the meantime it seems reasonable
enough to support a configuration mode where the section is entirely
omitted if the smallest module possible is desired.

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[pchickey]

Could we put a guard around addrs.push(range.clone(), &func.address_map.instructions); so we don't even allocate the memory for the address map when we aren't going to omit it?

[pchickey]

Also, should this imply WasmBacktraceDetails::Disable? What backtrace details will actually be emitted if the addr map isnt present?

[alexcrichton]

Could we put a guard around ...

Ah yes indeed!

Also, should this imply WasmBacktraceDetails::Disable?

While we won't get precise locations within functions (which also means no filenames/line numbers) we do still get the function names in the backtrace due to the .eh_frame section. I think because of that we probably don't want to forcibly disable backtraces for now, although in the future we could probably drop the .eh_frame section as well (at least on Unix) if it's a size concern.

[pchickey]

Thanks!