Makerules: fix MAKEFLAGS assignment for upcoming make-4.4 [BZ# 29564]

Makerules: fix MAKEFLAGS assignment for upcoming make-4.4 [BZ# 29564]

make-4.4 will add long flags to MAKEFLAGS variable:

    * WARNING: Backward-incompatibility!
      Previously only simple (one-letter) options were added to the MAKEFLAGS
      variable that was visible while parsing makefiles.  Now, all options
      are available in MAKEFLAGS.

This causes locale builds to fail when long options are used:

    $ make --shuffle
    ...
    make  -C localedata install-locales
    make: invalid shuffle mode: '1662724426r'

The change fixes it by passing eash option via whitespace and dashes.
That way option is appended to both single-word form and whitespace
separated form.

While at it fixed --silent mode detection in $(MAKEFLAGS) by filtering
out --long-options. Otherwise options like --shuffle flag enable silent
mode unintentionally. $(silent-make) variable consolidates the checks.

Resolves: BZ# 29564

CC: Paul Smith <psmith@gnu.org>
CC: Siddhesh Poyarekar <siddhesh@gotplt.org>
Signed-off-by: Sergei Trofimovich <slyich@gmail.com>
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>