[llvm] [Support] Use "using" instead of "typedef" (NFC) (PR #166130)

[Jakub Kuderski via llvm-commits]

================
@@ -146,17 +146,14 @@ typedef unsigned char   Boolean; /* 0 or 1 */
 #define UNI_UTF32_BYTE_ORDER_MARK_NATIVE 0x0000FEFF
 #define UNI_UTF32_BYTE_ORDER_MARK_SWAPPED 0xFFFE0000
 
-typedef enum {
-  conversionOK,           /* conversion successful */
-  sourceExhausted,        /* partial character in source, but hit end */
-  targetExhausted,        /* insuff. room in target for conversion */
-  sourceIllegal           /* source sequence is illegal/malformed */
-} ConversionResult;
-
-typedef enum {
-  strictConversion = 0,
-  lenientConversion
-} ConversionFlags;
+using ConversionResult = enum {
+  conversionOK,    /* conversion successful */
+  sourceExhausted, /* partial character in source, but hit end */
+  targetExhausted, /* insuff. room in target for conversion */
+  sourceIllegal    /* source sequence is illegal/malformed */
+};
+
+using ConversionFlags = enum { strictConversion = 0, lenientConversion };
----------------
kuhar wrote:

Why not name these enums instead?

https://github.com/llvm/llvm-project/pull/166130