libquadmath: Provide __BYTE_ORDER, __LITTLE_ENDIAN and __BIG_ENDIAN definitions

My earlier libquadmath change apparently broke mingw32 build, while on Linux
<bits/endian.h> is included and defines these, on Mingw apparently that isn't
the case, while soft-fp wants a guarantee that sfp-machine.h defines these.

2024-04-09  Jakub Jelinek  <[email protected]>

	* sfp-machine.h (__LITTLE_ENDIAN, __BIG_ENDIAN, __BYTE_ORDER): Define
	if __BYTE_ORDER isn't defined.

Author: jakubjelinek

libquadmath/sfp-machine.h

@@ -18,6 +18,11 @@
 #define _FP_NANSIGN_Q 1
 #define _FP_KEEPNANFRACP 1
 #define _FP_TININESS_AFTER_ROUNDING 0
+#ifndef __BYTE_ORDER
+#define __LITTLE_ENDIAN __ORDER_LITTLE_ENDIAN__
+#define __BIG_ENDIAN __ORDER_BIG_ENDIAN__
+#define __BYTE_ORDER __BYTE_ORDER__
+#endif
 #define _FP_DECL_EX \
   unsigned int fp_roundmode __attribute__ ((unused)) = FP_RND_NEAREST;
 #define FP_ROUNDMODE fp_roundmode