bug#43725: 28.0.50; Include feature/native-comp into master

[Eli Zaretskii]

One issue that I have in my notes about native-comp is the issue with
input encoding of the source we submit to the native-compiler.

The issue is this: our Lisp files are generally encoded in UTF-8.  But
there's no guarantee that GCC expects the source to be encoded in
UTF-8.  If the text we submit to libgccjit for compilation is in the
same encoding as the original .el files, then shouldn't we tell GCC
its actual encoding, to make sure non-ASCII text aren't mangled?