cmake: yaml: update timestamp on intermediate file save

file(GENERATE ...) does not update the output file if the content is
unchanged. Since the metadata in build_info.yml mostly depends on the
build configuration, the timestamp of the intermediate file does not get
updated on most rebuilds, while the final file does, due to immediate
file(WRITE ...) calls. Since the latter is newer, no post-process step
is executed and the file is left with commented genexes.

Touching the intermediate file ensures that the post-process step is
performed every time, even if the content is unchanged, restoring the
expected behavior.

Signed-off-by: Luca Burelli <[email protected]>

Author: pillo79

cmake/modules/yaml.cmake

@@ -534,6 +534,7 @@ function(yaml_save)
 
     to_yaml("${json_content}" 0 yaml_out TEMP_GENEX)
     FILE(GENERATE OUTPUT ${expanded_file} CONTENT "${yaml_out}")
+    FILE(TOUCH ${expanded_file}) # ensure timestamp is updated even if nothing changed
   endif()
 endfunction()