xray-color-helper.cpp - add missing implicit cmath header dependency. NFCI.

Noticed while investigating if we can remove an unnecessary MathExtras.h include from SmallVector.h (necessary for gcc builds but not MSVC)

tools/llvm-xray/xray-color-helper.cpp

@@ -13,6 +13,7 @@
 #include "xray-color-helper.h"
 #include "llvm/Support/FormatVariadic.h"
 #include "llvm/Support/raw_ostream.h"
+#include <cmath>
 
 using namespace llvm;
 using namespace xray;