Import unmodified NetBSD's libm for compiling with new libc.

As the current libc includes a libm implementation, with the new libc
this is needed. Unneeded (for the moment) archs have been removed.

lib/nbsd_libm/src/s_isinff.c

@@ -0,0 +1,27 @@
+/*
+ * Written by J.T. Conklin <jtc@NetBSD.org>.
+ * Public domain.
+ */
+
+#include <sys/cdefs.h>
+#if defined(LIBM_SCCS) && !defined(lint)
+__RCSID("$NetBSD: s_isinff.c,v 1.6 2003/07/26 19:25:06 salo Exp $");
+#endif
+
+/*
+ * isinff(x) returns 1 is x is inf, else 0;
+ * no branching!
+ */
+
+#include "math.h"
+#include "math_private.h"
+
+int
+isinff(float x)
+{
+	int32_t ix;
+	GET_FLOAT_WORD(ix,x);
+	ix &= 0x7fffffff;
+	ix ^= 0x7f800000;
+	return (ix == 0);
+}