File gr-hpsdr-fix-find-doxygen.patch of Package gr-hpsdr

diff -up gr-hpsdr-1.2.1/CMakeLists.txt.ddd gr-hpsdr-1.2.1/CMakeLists.txt
--- gr-hpsdr-1.2.1/CMakeLists.txt.ddd	2019-05-24 22:40:27.237770383 +0200
+++ gr-hpsdr-1.2.1/CMakeLists.txt	2019-05-24 22:51:35.168369377 +0200
@@ -106,6 +106,8 @@ if(NOT CPPUNIT_FOUND)
     message(FATAL_ERROR "CppUnit required to compile hpsdr")
 endif()
 
+find_package(Doxygen)
+
 ########################################################################
 # Setup the include and linker paths
 ########################################################################