fix: re-add build date to "About" page (#3464)

Co-authored-by: Felanbird <41973452+Felanbird@users.noreply.github.com>

src/CMakeLists.txt

@@ -593,6 +593,12 @@ set_target_properties(${LIBRARY_PROJECT}
     AUTOUIC ON
     )
 
+# Used to provide a date of build in the About page (for nightly builds). Getting the actual time of
+# compilation in CMake is a more involved, as documented in https://stackoverflow.com/q/24292898.
+# For CI runs, however, the date of build file generation should be consistent with the date of
+# compilation so this approximation is "good enough" for our purpose.
+string(TIMESTAMP cmake_gen_date "%Y-%m-%d")
+
 target_compile_definitions(${LIBRARY_PROJECT} PUBLIC
     CHATTERINO
     UNICODE
@@ -604,6 +610,8 @@ target_compile_definitions(${LIBRARY_PROJECT} PUBLIC
     CHATTERINO_GIT_HASH=\"${GIT_HASH}\"
     CHATTERINO_GIT_RELEASE=\"${GIT_RELEASE}\"
     CHATTERINO_GIT_COMMIT=\"${GIT_COMMIT}\"
+
+    CHATTERINO_CMAKE_GEN_DATE=\"${cmake_gen_date}\"
     )
 if (USE_SYSTEM_QTKEYCHAIN)
     target_compile_definitions(${LIBRARY_PROJECT} PUBLIC