Fix build with llvm-15
https://github.com/KDE/clazy/commit/20fca52da739ebefa47e35f6b338bb99a0da3cfe

Index: src/SourceCompatibilityHelpers.h
--- src/SourceCompatibilityHelpers.h.orig
+++ src/SourceCompatibilityHelpers.h
@@ -144,6 +144,21 @@ inline bool contains_lower(clang::StringRef haystack, 
 #endif
 }
 
+#if LLVM_VERSION_MAJOR >= 15
+using OptionalFileEntryRef = clang::Optional<clang::FileEntryRef>;
+#else
+using OptionalFileEntryRef = const clang::FileEntry*;
+#endif
+
+inline bool isAscii(clang::StringLiteral *lt)
+{
+#if LLVM_VERSION_MAJOR >= 15
+    return lt->isOrdinary();
+#else
+    return lt->isAscii();
+#endif
+}
+
 }
 
 #endif