Don't break when -lc and -sSIDE_MODULE are both passed

[hoodmane]

Resolves #16680.

Why is the current behavior broken?

Well what is "broken" from my specific perspective is the failure on the main branch of the added test:

  def test_lc_side_module(self):
    create_file('side.c', 'int sidey() { return 42; }')
    self.run_process([EMCC, '-sSIDE_MODULE', 'side.c', '-o', 'libside.so', '-lc'])

Rust, the libpng makefile, and various other tools pass -lc when they try to link shared libraries. It would be nice for it to work.

[sbc100]

Can you describe in the PR description what you mean by "don't break"? Why is broken with the current behaviour?

[sbc100]

I wonder if we should instead avoid adding native_lib to forced_stdlibs on line 4180, and if we should do it for all native system libs.. do we ever want to allow the side module to include a system library? Shouldn't they always get linking into the main module?

Perhaps we should at least do this for all default libraries (e.g. libc++, libcompiler_rt, etc)

[hoodmane]

Closing because the bug seems to have been fixed by other code changes.