stage2: upgrade musl libc stub file

This is the result of the work on tools/gen_stubs.zig. It now uses the
preprocessor to emit different symbols and sizes depending on the
architecture. The data is collected directly from multiple libc.so files
on disk built with upstream musl.

Closes #8178
Addresses #8896 for musl

There is still room for further improvement to this, which is to
put `.ds` directives after symbols that are not followed by aliases, to
avoid the potential problem of a linker believing that all symbols are
aliases of each other.