gitignore: Ignore Qt Creator project configuration files. NFC

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@363129 91177308-0d34-0410-b5e6-96231b3b80d8

.gitignore

@@ -45,6 +45,8 @@ autoconf/autom4te.cache
 /CMakeSettings.json
 # CLion project configuration
 /.idea
+# Qt Creator project configuration
+/CMakeLists.txt.user
 
 #==============================================================================#
 # Directories to ignore (do not add trailing '/'s, they skip symlinks).