mold: update to 1.5.1.

mold 1.5.1 is a new release of the high-speed linker. This version contains
only the following bug fix. We recommend upgrading from 1.5.0 if you are
being affected by this issue.

- We changed the memory layout to save both memory and disk space in 1.5.0.
  Even though the new layout works fine on most systems, the change made the
  linker to create unusable executables for systems with large pages.
  Specifically, if you specify a large number for the -z max-page-size
  option, the loader refused to execute it with the error while loading
  shared libraries: cannot apply additional memory protection after
  relocation: Cannot allocate memory error. We reverted our recent
  commits so that mold creates output files with the same memory layout
  as it did before 1.5.0.

(fcambus)