Fix LLVM 17 build

Change-Id: I74de56bdf76ae2db79eb6764a3b00c8b2524506a
Reviewed-on: https://codereview.kdab.com/c/kdab/code_browser/+/131307
Reviewed-by: Steffen Hansen <[email protected]>

Author: Waqar144

generator/preprocessorcallback.h

@@ -25,7 +25,7 @@
 #include <clang/Basic/Version.h>
 #include <clang/Lex/MacroInfo.h>
 #include <clang/Lex/PPCallbacks.h>
-#if CLANG_VERSION_MAJOR >= 15
+#if CLANG_VERSION_MAJOR == 15
 #include <llvm/ADT/Optional.h>
 #endif