[Patch-gnuradio] Fixing the build of gnuradio on Gentoo

[Maciej Grela]

Hi,

When trying to build the gnuradio from git master on my Gentoo box I
stumbled upon the following error:

-- ######################################################
-- # Gnuradio disabled components                       
-- ######################################################
--   * doxygen
--   * gnuradio-companion
--   * gr-comedi
--   * gr-qtgui
--   * gr-uhd
--   * gr-shd
--   * gr-wxgui
-- 
-- Using install prefix: /usr/local
-- Building for version: 3.6.0git-10-g6a1e9783 / 3.6.0git
CMake Error: The following variables are used in this project, but they
are set to NOTFOUND.
Please set them or make sure they are set and tested correctly in the
CMake files:
JACK_INCLUDE_DIR
   used as include directory in directory
/home/grela/Dokumenty/devel/gnuradio/gr-audio/lib

-- Configuring incomplete, errors occurred!


The reason for it is that the current FindJack cmake module sets
JACK_FOUND when a libjack.so library is found. This fact is not a clear
indication that you can build anything using JACK - you also need the
header files. On Gentoo, a 32-bit compatibility libjack.so library is
provided in the system by the app-emulation/emul-linux-x86-soundlibs
compatibility package, but the header files are not there - therefore
this error occurs. I've changed the FindJack cmake module to set
JACK_FOUND only when both the library and header files are present. This
approach is more robust in my opinion.

The attached patch has been formatted with git format-patch. Will you
consider applying it to the main repo ?

Best regards,

0001-cmake-Improve-JACK-detection-module.patch
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