File fix-cmake-vars.patch of Package AppImageUpdate

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -9,12 +9,14 @@
 # WARNING: this value will be stored in the CMake cache
 # to update it, you will have to reset the CMake cache
 # (doesn't matter for CI builds like Travis for instance, where there's no permanent CMake cache)
-execute_process(
-    COMMAND git rev-parse --short HEAD
-    WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}
-    OUTPUT_VARIABLE GIT_COMMIT
-    OUTPUT_STRIP_TRAILING_WHITESPACE
-)
+if (NOT GIT_COMMIT)
+    execute_process(
+        COMMAND git rev-parse --short HEAD
+        WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}
+        OUTPUT_VARIABLE GIT_COMMIT
+        OUTPUT_STRIP_TRAILING_WHITESPACE
+    )
+endif()
 
 # set version and build number
 set(VERSION 1-alpha)
@@ -25,11 +27,7 @@
 endif()
 
 # get current date
-execute_process(
-    COMMAND env LC_ALL=C date -u "+%Y-%m-%d %H:%M:%S %Z"
-    OUTPUT_VARIABLE DATE
-    OUTPUT_STRIP_TRAILING_WHITESPACE
-)
+string(TIMESTAMP DATE "%Y-%m-%d %H:%M:%S" UTC)
 
 option(ENABLE_SANITIZERS "Enable builds using sanitizers" off)