kbuild: consolidate command line escaping

While the recent change to also escape # symbols when storing C-file
compilation command lines was helpful, it should be in effect for all
command lines, as much as the dollar escaping should be in effect for
C-source compilation commands. Additionally, for better readability and
maintenance, consolidating all the escaping (single quotes, dollars,
and now sharps) was also desirable.

Signed-Off-By: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>