BUILD: Set timezone on release date for reproducibility

To make the build reproducible, it's needed to set the timezone as
otherwise the date could vary based on the timezone of the build server.

Link: https://bugs.debian.org/1060254

auxiliary_files/CMakeLists.txt

@@ -8,7 +8,7 @@ include(pkg-utils)
 
 if(NOT BUILD_RELEASE_DATE)
 	# If BUILD_RELEASE_DATE has not been set, default to time of build
-	string(TIMESTAMP BUILD_RELEASE_DATE "%Y-%m-%d")
+	string(TIMESTAMP BUILD_RELEASE_DATE "%Y-%m-%d" UTC)
 endif()
 
 if(overlay)