enable [[msvc::flatten]] on msvc as learned on twitter

Author: hanickadot

include/ctre/utility.hpp

@@ -24,7 +24,7 @@
 
 #ifdef _MSC_VER
 #define CTRE_FORCE_INLINE __forceinline
-#define CTRE_FLATTEN
+#define CTRE_FLATTEN [[msvc::flatten]]
 #else
 #define CTRE_FORCE_INLINE inline __attribute__((always_inline))
 #define CTRE_FLATTEN __attribute__((flatten))

single-header/ctre-unicode.hpp

@@ -1408,7 +1408,7 @@ struct pcre {
 
 #ifdef _MSC_VER
 #define CTRE_FORCE_INLINE __forceinline
-#define CTRE_FLATTEN
+#define CTRE_FLATTEN [[msvc::flatten]]
 #else
 #define CTRE_FORCE_INLINE inline __attribute__((always_inline))
 #define CTRE_FLATTEN __attribute__((flatten))

single-header/ctre.hpp

@@ -1405,7 +1405,7 @@ struct pcre {
 
 #ifdef _MSC_VER
 #define CTRE_FORCE_INLINE __forceinline
-#define CTRE_FLATTEN
+#define CTRE_FLATTEN [[msvc::flatten]]
 #else
 #define CTRE_FORCE_INLINE inline __attribute__((always_inline))
 #define CTRE_FLATTEN __attribute__((flatten))