Move non-constexpr function to .cpp file

wpilibc/src/main/native/cpp/util/Color.cpp

@@ -0,0 +1,13 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#include "frc/util/Color.h"
+
+using namespace frc;
+
+std::string Color::HexString() const {
+  return fmt::format("#{:02X}{:02X}{:02X}", static_cast<int>(255.0 * red),
+                     static_cast<int>(255.0 * green),
+                     static_cast<int>(255.0 * blue));
+}

wpilibc/src/main/native/cpp/util/Color8Bit.cpp

@@ -0,0 +1,11 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#include "frc/util/Color8Bit.h"
+
+using namespace frc;
+
+std::string Color8Bit::HexString() const {
+  return fmt::format("#{:02X}{:02X}{:02X}", red, green, blue);
+}

wpilibc/src/main/native/include/frc/util/Color.h

@@ -851,11 +851,7 @@ class Color {
    *
    * @return a string of the format <tt>\#RRGGBB</tt>
    */
-  std::string HexString() const {
-    return fmt::format("#{:02X}{:02X}{:02X}", static_cast<int>(255.0 * red),
-                       static_cast<int>(255.0 * green),
-                       static_cast<int>(255.0 * blue));
-  }
+  std::string HexString() const;
 
   double red = 0.0;
   double green = 0.0;

wpilibc/src/main/native/include/frc/util/Color8Bit.h

@@ -107,9 +107,7 @@ class Color8Bit {
    *
    * @return a string of the format <tt>\#RRGGBB</tt>
    */
-  std::string HexString() const {
-    return fmt::format("#{:02X}{:02X}{:02X}", red, green, blue);
-  }
+  std::string HexString() const;
 
   int red = 0;
   int green = 0;