Implemented ARCHIVE_OUTPUT_DIRECTORY for uf2 output in CMake. Fixes earlephilhower#1012 (earlephilhower#1036)

* Added ARCHIVE_OUTPUT_DIRECTORY to uf2 output in CMake

This Commit enables the use of the ARCHIVE_OUTPUT_DIRECTORY target
properties in CMake for the generation of uf2 files.

The changeset in lines 47..51 is necessary due to CMake not
automatically creating the ARCHIVE_OUTPUT_DIRECTORY if no archive target
is present.

* rework cmake changes to make it friendler for non absolute paths

Co-authored-by: Graham Sanderson <graham.sanderson@raspberrypi.com>

Author: dtreffenstaedt

tools/CMakeLists.txt

@@ -44,12 +44,21 @@ function(pico_generate_pio_header TARGET PIO)
 endfunction()
 
 function(pico_add_uf2_output TARGET)
+    get_target_property(${TARGET}_archive_directory ${TARGET} ARCHIVE_OUTPUT_DIRECTORY)
+    if (${TARGET}_archive_directory)
+        get_filename_component(output_path "${${TARGET}_archive_directory}"
+                REALPATH BASE_DIR "${CMAKE_CURRENT_BINARY_DIR}")
+        file(MAKE_DIRECTORY "${output_path}")
+        set(output_path "${output_path}/")
+    else()
+        set(output_path "")
+    endif()
     if (NOT ELF2UF2_FOUND)
         set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} ${PICO_SDK_PATH}/tools)
         find_package(ELF2UF2)
     endif()
     if (ELF2UF2_FOUND)
         add_custom_command(TARGET ${TARGET} POST_BUILD
-                COMMAND ELF2UF2 $<TARGET_FILE:${TARGET}> $<IF:$<BOOL:$<TARGET_PROPERTY:${TARGET},OUTPUT_NAME>>,$<TARGET_PROPERTY:${TARGET},OUTPUT_NAME>,$<TARGET_PROPERTY:${TARGET},NAME>>.uf2)
+            COMMAND ELF2UF2 $<TARGET_FILE:${TARGET}> ${output_path}$<IF:$<BOOL:$<TARGET_PROPERTY:${TARGET},OUTPUT_NAME>>,$<TARGET_PROPERTY:${TARGET},OUTPUT_NAME>,$<TARGET_PROPERTY:${TARGET},NAME>>.uf2)
     endif()
 endfunction()