llext: move current test to a hello_world subdir

In preparation for multiple tests, move the current hello_world test
to its own subdirectory. Also, merge the llext compilation in the
parent CMakeLists.txt.

Signed-off-by: Luca Burelli <l.burelli@arduino.cc>

tests/subsys/llext/hello_world/CMakeLists.txt

@@ -3,7 +3,7 @@
 
 cmake_minimum_required(VERSION 3.20.0)
 find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
-project(hello_world)
+project(llext_hello_world_test)
 
 if(NOT CONFIG_LLEXT_TEST_HELLO)
   # Test disabled, do nothing
@@ -12,14 +12,26 @@ elseif(CONFIG_MODULES AND NOT CONFIG_LLEXT_TEST_HELLO STREQUAL "m")
   message(FATAL_ERROR "CONFIG_LLEXT_TEST_HELLO must be set to 'm' when CONFIG_MODULES is enabled")
 else()
 
-  set(llext_src_file ${PROJECT_SOURCE_DIR}/hello_world.c)
-  set(llext_bin_file ${PROJECT_BINARY_DIR}/hello_world.llext)
+  target_sources(app PRIVATE
+    src/test/test_llext_simple.c
+  )
+
+  target_include_directories(app PRIVATE
+    ${ZEPHYR_BASE}/include
+    ${ZEPHYR_BASE}/kernel/include
+    ${ZEPHYR_BASE}/arch/${ARCH}/include
+  )
+
+  # Compile a simple hello world llext to an include file
+  set(llext_src_file ${PROJECT_SOURCE_DIR}/src/llext/hello_world.c)
+  set(llext_bin_file ${ZEPHYR_BINARY_DIR}/hello_world.llext)
+  set(llext_inc_file ${ZEPHYR_BINARY_DIR}/include/generated/hello_world.inc)
 
   add_llext_target(hello_world_llext
     OUTPUT  ${llext_bin_file}
     SOURCES ${llext_src_file}
   )
 
-  set(HELLO_WORLD_LLEXT ${llext_bin_file} PARENT_SCOPE)
+  generate_inc_file_for_target(app ${llext_bin_file} ${llext_inc_file})
 
 endif()