Implement test for system byteswap.h header file.

The result of this check is required by libavutil library.
If it is not defined the library would try to implement its own
byte swapping routines in bswap.h . As the routines are with same names, 
if included, the system definition would replace the function names with
the macros. The result can not be compiled and looks like this:

# 42 "../libavutil/bswap.h"
-static av_always_inline uint16_t bswap_16(uint16_t x)
+static __attribute__((always_inline)) inline uint16_t (__extension__ ({ register unsigned short int __v, __x = (uint16_t x); if (__builtin_constant_p (__x)) __v = ((((__x) >> 8) & 0xff) | (((__x) & 0xff) << 8)); else __asm__ ("rorw $8, %w0" : "=r" (__v) : "0" (__x) : "cc"); __v; }))


git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@25989 b3059339-0415-0410-9bf9-f77b7e298cf2

configure

@@ -3008,6 +3008,21 @@ fi
 echores "$_alloca"
 
 
+echocheck "byteswap.h"
+cat > $TMPC << EOF
+#include <byteswap.h>
+int main(void) {  bswap_16(0); return 0; }
+EOF
+_byteswap_h=no
+cc_check && _byteswap_h=yes
+if cc_check ; then
+  _def_byteswap_h='#define HAVE_BYTESWAP_H 1'
+else
+  _def_byteswap_h='#undef HAVE_BYTESWAP_H'
+fi
+echores "$_byteswap_h"
+
+
 echocheck "mman.h"
 cat > $TMPC << EOF
 #include <sys/types.h>
@@ -8024,6 +8039,9 @@ $_def_asmalign_pot
 /* Define this if your system has the "alloca.h" header file */
 $_def_alloca
 
+/* Define this if your system has the "byteswap.h" header file */
+$_def_byteswap_h
+
 /* Define this if your system has the "sys/mman.h" header file */
 $_def_mman
 $_def_mman_has_map_failed