[llvm] [NFC] Various Cleanup in StackColoring, StackSlotColoring, LiveStacks (PR #143931)

[Matt Arsenault via llvm-commits]

================
@@ -795,6 +795,49 @@ using stack_float_t = volatile float;
 using stack_float_t = float;
 #endif
 
+/// Returns the number of digits in the given integer.
+inline int NumDigits(uint64_t N) {
----------------
arsenm wrote:

Can you make it clear this is base 10 digits in the name? Also we could do something like https://stackoverflow.com/a/25934909 that @stephentyrone apparently suggested 

https://github.com/llvm/llvm-project/pull/143931