lib: Add include directory to open_amp-static target

Include a header directory in the open_amp-static target, enabling
building and linking static library using CMake subdirectory.

Signed-off-by: Taras Zaporozhets <zaporozhets.taras@gmail.com>

lib/CMakeLists.txt

@@ -61,6 +61,7 @@ else (WITH_ZEPHYR)
   if (WITH_STATIC_LIB)
     set (_lib ${OPENAMP_LIB}-static)
     add_library (${_lib} STATIC ${_sources})
+    target_include_directories(${_lib} PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/include)
     install (TARGETS ${_lib} ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR})
     set_target_properties (${_lib} PROPERTIES
       OUTPUT_NAME       "${OPENAMP_LIB}"