Update unix Makefile template to handle paths with spaces

Fixes #4668 (on unix-like platforms)

Testing:

  rm -rf "$HOME/tmp/beforespace afterspace"
  ./Configure -Werror --strict-warnings --prefix="$HOME/tmp/beforespace afterspace"
  make -j6 update
  make -j6
  make install
  make test

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Todd Short <todd.short@me.com>
(Merged from #21821)