Add GNU definition for QNX toolchain

Author: pablorcum

toolbox/overlay-triplets/qnx-toolchain.cmake

@@ -56,9 +56,10 @@ set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE BOTH)
 
 # QNX doesn’t use glibc; some ports may need feature tests or POSIX settings.
 add_compile_definitions(_QNX_SOURCE)
+add_compile_definitions(__GNU__)
 
 # Set fPIC flag
 set(CMAKE_POSITION_INDEPENDENT_CODE ON)
 
 # Do not treat include directories from the interfaces of consumed Imported Targets as system directories.
-set(CMAKE_NO_SYSTEM_FROM_IMPORTED ON)
+set(CMAKE_NO_SYSTEM_FROM_IMPORTED ON)