with the new autotools-based build system, Pd also generates a pkg-config  file (it's pd.pc, generated from pd.pc.in).
the purpose of this file is to sease compilation of externals in a standardized way, by providing information on where to find header files (e.g. /usr/include/pd) and which libraries we need to link too (e.g. link against pd.lib" on w32, but not on other platforms)
unfortunately i was a bit too eager, when i first created this file, adding lots of flags and bells and whistles, which have turned out to be more confusing than helping.
attached patch therefore simplifies the generated pd.pc to only hold the relevant information (see in-patch description for more details)