jack installs a pkg-config file, allowing the autotools
to detect its presence painlessly. in an autoconf.{ac,in}
file:PKG_CHECK_MODULE(jack,...) should work - i can't check the precise command because my computers are dead, but read up on pkg-config, its a superb system for this kind of thing and is thankfully replacing the morass of foo-config scripts that has been growing for the last few years. --p
