Get back Boost recipe in chapter 3 with PGI

Author: robertodr

chapter-03/recipe-08/cxx-example/menu.yml

@@ -3,11 +3,10 @@ appveyor-vs:
     - BOOST_ROOT: 'C:\Libraries\boost_1_67_0'
     - CMAKE_CXX_FLAGS: '-DBOOST_ALL_NO_LIB'  
 
-# PGI and Boost do not get along
 circle-pgi:
-  skip_generators:
-    - 'Unix Makefiles'
-    - 'Ninja'
+  definitions:
+   - BOOST_INCLUDEDIR: '/usr/include/boost'
+   - BOOST_LIBRARYDIR: '/usr/lib/x86_64-linux-gnu'
 
 travis-osx:
   definitions: