mold: update to 1.4.0.

New features:

- Initial support for the 32-bit RISC-V (RV32) has landed.
- mold now demangles Rust symbols in error messages thanks to eddyb's
  rust-demangle.c.
- --export-dynamic-symbol and --export-dynamic-symbol-list are now supported
  for the sake of compatibility with LLVM lld. With these options, you
  can specify symbols that should be exported using glob pattern.
- [x86-64] PLT entries created by mold now always begins with ENDBR64
  instruction to improve compatibility with Intel IBT (Indirect Branch
  Tracking.)

Bug fixes and compatibility improvements:

- mold now defines __dso_handle symbol. The lack of this linker-synthesized
  symbol caused a link error with GCC in some environments.

(fcambus)