BUILD_PKG_CONFIG installs files across project directories into
$(JWBDIR) because of this:
BUILD_PKG_CONFIGDIR = $(JWBDIR)/pkgconfig
The concept is currently not used by any downstream project anymore,
hence it lacks sufficient testing at this point. Moreover, it breaks
building repos which are sandboxed to their own root directory,
because it tries to install the generated .pc file back into
$(JWBDIR). The concept itself isn't entirely off, so leave the code
in, disabled, with a comment.
Signed-off-by: Jan Lindemann <jan@janware.com>