Revert "ByteOrder.h: remove use of __builtin_bswap16."

This reverts commit 040dc2eebc.

headers/os/support/ByteOrder.h

@@ -29,11 +29,6 @@ typedef enum {
 #	define ntohl(x) B_BENDIAN_TO_HOST_INT32(x)
 #	define htons(x) B_HOST_TO_BENDIAN_INT16(x)
 #	define ntohs(x) B_BENDIAN_TO_HOST_INT16(x)
-
-static inline uint16 __swap_int16(uint16 arg)
-{
-	return (arg >> 8) | (arg << 8);
-}
 #endif
 
 /* always swap macros */
@@ -128,9 +123,11 @@ extern float  __swap_float(float arg);
 #if __GNUC__ >= 4
 #define __swap_int64(arg)	__builtin_bswap64(arg)
 #define __swap_int32(arg)	__builtin_bswap32(arg)
+#define __swap_int16(arg)	__builtin_bswap16(arg)
 #else
 extern uint64 __swap_int64(uint64 arg);
 extern uint32 __swap_int32(uint32 arg);
+extern uint16 __swap_int16(uint16 arg);
 #endif
 
 #ifdef __cplusplus

headers/posix/netinet/in.h

@@ -31,10 +31,6 @@ typedef uint32_t in_addr_t;
 #	else
 		extern unsigned int __swap_int32(unsigned int);	/* private */
 #	endif
-	static inline uint16_t __swap_int16(uint16_t arg)
-	{
-		return (arg >> 8) | (arg << 8);
-	}
 	extern uint16_t __swap_int16(uint16_t);	/* private */
 #	if BYTE_ORDER == LITTLE_ENDIAN
 #		define htonl(x) ((uint32_t)__swap_int32(x))

src/build/libroot/byteorder.cpp

@@ -7,6 +7,12 @@
 
 #include <ByteOrder.h>
 
+uint16
+__swap_int16(uint16 value)
+{
+	return (value >> 8) | (value << 8);
+}
+
 uint32
 __swap_int32(uint32 value)
 {