[Support] Use hexdigit instead of manually coding the same thing. NFC

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@259762 91177308-0d34-0410-b5e6-96231b3b80d8

Author: topperc

lib/Support/raw_ostream.cpp

@@ -171,8 +171,8 @@ raw_ostream &raw_ostream::write_hex(unsigned long long N) {
   char *CurPtr = EndPtr;
 
   while (N) {
-    uintptr_t x = N % 16;
-    *--CurPtr = (x < 10 ? '0' + x : 'a' + x - 10);
+    unsigned char x = static_cast<unsigned char>(N) % 16;
+    *--CurPtr = hexdigit(x, /*LowerCase*/true);
     N /= 16;
   }