bsd.man.mk doesn't include ${.CURDIR}/../Makefile.inc.
Removed GDBDIR-redefinition-prevention ifdef. It hasn't done anothing
for a long time, if ever. The directory is defined to the same value in
each subdir and had the same value because all subdirs are at the same
level. Keep defining it in the subdirs since that is more flexible and
no more verbose.
Prepare to inherit BINDIR by including ../Makefile.inc.
