build: Quote redirections when echoing commands.

build: Quote redirections when echoing commands.

Without this, "make --directory=doc V=1 keymap-defaults.txt"
would not display the command it runs, because the command is

LC_ALL=C LANGUAGE=en /home/Kalle/src/elinks-0.12/doc/tools/keys2doc /home/Kalle/src/elinks-0.12/src/config/kbdbind.c keymap-defaults.txt > keymap-defaults.txt

and the build system would run

echo LC_ALL=C LANGUAGE=en /home/Kalle/src/elinks-0.12/doc/tools/keys2doc /home/Kalle/src/elinks-0.12/src/config/kbdbind.c keymap-defaults.txt > keymap-defaults.txt && LC_ALL=C LANGUAGE=en /home/Kalle/src/elinks-0.12/doc/tools/keys2doc /home/Kalle/src/elinks-0.12/src/config/kbdbind.c keymap-defaults.txt > keymap-defaults.txt

so, the initial echo was redirected to keymap-defaults.txt too,
and then overwritten with the intended output.  Now, the build
system instead runs

echo 'LC_ALL=C LANGUAGE=en /home/Kalle/src/elinks-0.12/doc/tools/keys2doc /home/Kalle/src/elinks-0.12/src/config/kbdbind.c keymap-defaults.txt > keymap-defaults.txt' && LC_ALL=C LANGUAGE=en /home/Kalle/src/elinks-0.12/doc/tools/keys2doc /home/Kalle/src/elinks-0.12/src/config/kbdbind.c keymap-defaults.txt > keymap-defaults.txt

which echoes the redirection instead of executing it.  This change
also makes the output correctly preserve quotes in some other rules.