PKG-CONFIG error in Mac OS X

[fstrozzi]

There is this error in the compilation of FASTX package on Mac OS X when pkg-config is not present:

configure: error: The pkg-config script could not be found or is too old. Make sure it
is in your PATH or set the PKG_CONFIG environment variable to the full
path to pkg-config.

Alternatively, you may set the environment variables GTEXTUTILS_CFLAGS
and GTEXTUTILS_LIBS to avoid the need to call pkg-config.
See the pkg-config man page for more details.

Setting those env variables does not seem to fix the problem.