[libc] Move VA_ARG_COUNT() macro to stdarg.h

Make the non-standard but extremely useful macro VA_ARG_COUNT()
available outside of dhcp.h.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/dhcp.h

 FILE_LICENCE ( GPL2_OR_LATER );
 
 #include <stdint.h>
+#include <stdarg.h>
 #include <ipxe/in.h>
 #include <ipxe/list.h>
 #include <ipxe/refcnt.h>
 
 /** @} */
 
-/**
- * Count number of arguments to a variadic macro
- *
- * This rather neat, non-iterative solution is courtesy of Laurent
- * Deniau.
- *
- */
-#define _VA_ARG_COUNT(  _1,  _2,  _3,  _4,  _5,  _6,  _7,  _8,		\
-		        _9, _10, _11, _12, _13, _14, _15, _16,		\
-		       _17, _18, _19, _20, _21, _22, _23, _24,		\
-		       _25, _26, _27, _28, _29, _30, _31, _32,		\
-		       _33, _34, _35, _36, _37, _38, _39, _40,		\
-		       _41, _42, _43, _44, _45, _46, _47, _48,		\
-		       _49, _50, _51, _52, _53, _54, _55, _56,		\
-		       _57, _58, _59, _60, _61, _62, _63,   N, ... ) N
-#define VA_ARG_COUNT( ... )						\
-	_VA_ARG_COUNT ( __VA_ARGS__, 					\
-			63, 62, 61, 60, 59, 58, 57, 56,			\
-			55, 54, 53, 52, 51, 50, 49, 48,			\
-			47, 46, 45, 44, 43, 42, 41, 40,			\
-			39, 38, 37, 36, 35, 34, 33, 32,			\
-			31, 30, 29, 28, 27, 26, 25, 24,			\
-			23, 22, 21, 20, 19, 18, 17, 16,			\
-			15, 14, 13, 12, 11, 10,  9,  8,			\
-			 7,  6,  5,  4,  3,  2,  1,  0 )
-
 /** Construct a DHCP option from a list of bytes */
 #define DHCP_OPTION( ... ) VA_ARG_COUNT ( __VA_ARGS__ ), __VA_ARGS__
 

src/include/stdarg.h

 #define va_end( ap ) __builtin_va_end ( ap )
 #define va_copy( dest, src ) __builtin_va_copy ( dest, src )
 
+/**
+ * Count number of arguments to a variadic macro
+ *
+ * This rather neat, non-iterative solution is courtesy of Laurent
+ * Deniau.
+ *
+ */
+#define _VA_ARG_COUNT(  _1,  _2,  _3,  _4,  _5,  _6,  _7,  _8,		\
+		        _9, _10, _11, _12, _13, _14, _15, _16,		\
+		       _17, _18, _19, _20, _21, _22, _23, _24,		\
+		       _25, _26, _27, _28, _29, _30, _31, _32,		\
+		       _33, _34, _35, _36, _37, _38, _39, _40,		\
+		       _41, _42, _43, _44, _45, _46, _47, _48,		\
+		       _49, _50, _51, _52, _53, _54, _55, _56,		\
+		       _57, _58, _59, _60, _61, _62, _63,   N, ... ) N
+#define VA_ARG_COUNT( ... )						\
+	_VA_ARG_COUNT ( __VA_ARGS__, 					\
+			63, 62, 61, 60, 59, 58, 57, 56,			\
+			55, 54, 53, 52, 51, 50, 49, 48,			\
+			47, 46, 45, 44, 43, 42, 41, 40,			\
+			39, 38, 37, 36, 35, 34, 33, 32,			\
+			31, 30, 29, 28, 27, 26, 25, 24,			\
+			23, 22, 21, 20, 19, 18, 17, 16,			\
+			15, 14, 13, 12, 11, 10,  9,  8,			\
+			 7,  6,  5,  4,  3,  2,  1,  0 )
+
 #endif /* _STDARG_H */