Add configure flag to exclude emscripten_syscalls.c

[hoodmane]

Pyodide doesn't want to include emscripten_syscalls.c in the build since it links a different version of it, so we should add a configure flag to drop it.

Linked PRs

• gh-154465: Add configure flag to exclude emscripten_syscalls.c #154466

[freakboy3742]

Closing since #154465 has been merged.