[Savannah #20501] Handle adding -r/-R to MAKEFLAGS in the makefile.

[Savannah #20501] Handle adding -r/-R to MAKEFLAGS in the makefile.

If -R is set in the makefile and not the command line, then go through all the
default variables and undefine them.  If -r is set in the makefile and not in
the command line, then remove all .SUFFIX prefixes (unless the user set it)
and SUFFIX variable setting.  In -p mode don't print builtins.