pkg-config info not found

[osrf-migration]

Original report (archived issue) by Brian Gerkey (Bitbucket: Brian Gerkey, GitHub: gerkey).

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When building Citadel from source on Ubuntu 18.04 (ign-launch is on the ign-launch2 branch), I get this warning (the build succeeds):

--- stderr: ignition-launch2
CMake Warning (dev) at /home/gerkey/code/rse/ign/install/share/cmake/ignition-cmake2/cmake2/IgnUtils.cmake:378 (message):
   -- THIS MESSAGE IS INTENDED FOR IGNITION-LAUNCH AUTHORS --
      (IF YOU SEE THIS, PLEASE REPORT IT)  Could not find pkg-config information for ignition-tools.  It was not
  provided by the find-module for the package, nor was it explicitly passed
  into the call to ign_find_package(~).  This is most likely an error in this
  project's use of ign-cmake.
Call Stack (most recent call first):
  CMakeLists.txt:49 (ign_find_package)
This warning is for project developers.  Use -Wno-dev to suppress it.

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