make :Q breakage

[Valery Ushakov <uwe%stderr.spb.ru@localhost>]

Recent commit to make:

  http://mail-index.netbsd.org/source-changes/2018/05/24/msg095440.html

  Since ${MAKE} converts $$ -> $ during parsing we need to put it back to
  preserve the original variable value with :Q.

broke pkgsrc as tool wrappers it creates now contain code like, e.g.

  /bin/mkdir -p "$$@"

instead of the intended "$@"


A minimal test to demonstrate the problem is

FOO=doit "$$@"
default:
        foo=${FOO:Q}; echo foo=$$foo


$ make -f q.mk 
foo=doit\ \"\$\$@\"; echo foo=$foo
foo=doit "$$@"

-uwe