Fix nasa#1339, add doc-prebuild dependency

When building as part of CFE/CFS, register the osal header list file
(osal-public-api.doxyfile) as a dependency of the doc-prebuild abstract
target.  This way, CFE and any other CFS apps that refer to the OSAL
headers in their documentation can easily ensure that this (and any
other file produced by other modules) exist prior to attempting to run
doxygen.

docs/src/CMakeLists.txt

@@ -68,17 +68,25 @@ endif ()
 # Generate the list of actual header files from the directories specified.  This is done
 # as a target that runs a separate script such that generator expressions can be evaluated.
 # This is done as a custom target such that it runs and gets updated every build
-add_custom_target(osal_public_api_headerlist 
+add_custom_command(OUTPUT "${CMAKE_BINARY_DIR}/docs/osal-public-api.doxyfile"
     COMMAND ${CMAKE_COMMAND}
         -DINCLUDE_DIRECTORIES="${OSAL_API_INCLUDE_DIRECTORIES}"
         -DCOMPILE_DEFINITIONS="${OSAL_API_COMPILE_DEFINITIONS}"
         -DINPUT_TEMPLATE="${CMAKE_CURRENT_SOURCE_DIR}/osal-public-api.doxyfile.in"
         -DOUTPUT_FILE="${CMAKE_BINARY_DIR}/docs/osal-public-api.doxyfile"
         -P "${CMAKE_CURRENT_SOURCE_DIR}/generate-public-api-doxyfile.cmake"
-    BYPRODUCTS "${CMAKE_BINARY_DIR}/docs/osal-public-api.doxyfile"
     WORKING_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}"
 )
 
+add_custom_target(osal_public_api_headerlist
+    DEPENDS "${CMAKE_BINARY_DIR}/docs/osal-public-api.doxyfile")
+
+# if building as part of CFS, then generate the doxygen header list as part of the prebuild step
+# The "doc-prebuild" target is defined by the CFS build, and thus will not exist if building standalone
+if (TARGET doc-prebuild)
+   add_dependencies(doc-prebuild osal_public_api_headerlist)
+endif ()
+
 file(TO_NATIVE_PATH ${CMAKE_CURRENT_BINARY_DIR}/osal-apiguide-warnings.log OSAL_NATIVE_LOGFILE)
 file(TO_NATIVE_PATH ${CMAKE_BINARY_DIR}/docs/osal-common.doxyfile OSAL_NATIVE_COMMON_CFGFILE)
 file(TO_NATIVE_PATH ${CMAKE_CURRENT_BINARY_DIR}/osal-apiguide.doxyfile OSAL_NATIVE_APIGUIDE_CFGFILE)