gdb/data-directory: silence output from mkinstalldirs script

gdb/data-directory: silence output from mkinstalldirs script

After my recent changes the data-directory build now uses
silent-rules.mk to reduce the output.

One problem that remains was the use of mkinstalldirs by stamp-python
and stamp-guile for creating some directories, the mkinstalldirs
prints some messages, so we're left with output like this:

    GEN    stamp-python
  mkdir -p -- ./python/gdb
  mkdir -p -- ./python/gdb/command
  mkdir -p -- ./python/gdb/dap
  mkdir -p -- ./python/gdb/function
  mkdir -p -- ./python/gdb/printer

I was looking at adding a --silent option to the mkinstalldirs script,
however, when I took a look at the automake package (which is where
mkinstalldirs comes from) it turns out that mkinstalldirs is
deprecated, at the advice is to use 'install-sh -d' instead.

Just like we carry mkinstalldirs in the top-level directory, we also
carry install-sh, and a version of install-sh which supports the -d
flag.

And best of all, 'install-sh -d' doesn't appear to print any of the
information messages to stdout that mkinstalldirs does, so if we
switch to use that, we get a quieter build.

There should be no changes in what is built after this commit

Approved-By: Tom Tromey <tom@tromey.com>