honor pkg-config for pd

[umlaeute]

Pd provides a pkg-config script, which could be utilized to guess the correct flags

$ pkg-config --cflags pd
-DPD -I/usr/include/pd
$ pkg-config --libs pd
$

[katjav]

On which platform(s) would this work by default?

Some time ago I was looking into pkg-config as a method to find parameters for dependencies that Pd libs may have. It would be very convenient if a makefile doesn't need to specify such flags and paths. It seems that pkg-config is even available for MinGW but not trivial to install (as stated in http://www.mingw.org/wiki/FAQ). A makefile can't rely on it, so what should it do when pkg-config is not installed? The flags should be specified in the makefile after all, and the convenience is gone.

[umlaeute]

it should work on all platforms that have pkg-config installed (and Pd's .pc files installed in a place where pkg-config can find them).
something like the following (untested code):

 usepkgconfig := $(shell which pkg-config && pkg-config --exists pd && echo "yes")

(which platform this actually could be, should be left to the user)

[danomatika]

The above check would work fine on platforms that have it installed. Simply fall back to current defaults on those that don't.