Support multiple functions in same module sharing an implementation

[atdrendel]

Currently, if multiple named exported functions share a single implementation, Wasm3 only exposes one of the exported functions to clients. This is because only the first name is saved to M3Function inside ParseSection_Export()

if (not io_module->functions [index].name)
{
  io_module->functions [index].name = utf8;
  utf8 = NULL; // ownership transfered to M3Function
}

A simple WebAssembly module illustrates this problem:

(module
  (type (;0;) (func (result i32)))
  (func (;0;) (type 0) (result i32)
    i32.const 42)
  (export "first" (func 0))
  (export "second" (func 0)))

If you try to use m3_FindFunction() to find first(), you will succeed. However, trying to find second() will fail.

We have run into this problem when using Wasm3 with Libsodium. Libsodium exposes a number of different functions that wrap private constants, some of which are equal. These functions are all compiled down into the same WebAssembly function implementation with different exported names.

[atdrendel]

I've opened this pull request with a possible fix.

[vshymanskyy]

merged