mips: add single-instruction math functions

SQRT.fmt exists on MIPS II+ (float), MIPS III+ (double).

ABS.fmt exists on MIPS I+ but only cores with ABS2008 flag in FCSR
implement the required behaviour.

src/math/mips/fabs.c

+#if !defined(__mips_soft_float) && defined(__mips_abs2008)
+
+#include <math.h>
+
+double fabs(double x)
+{
+	double r;
+	__asm__("abs.d %0,%1" : "=f"(r) : "f"(x));
+	return r;
+}
+
+#else
+
+#include "../fabs.c"
+
+#endif

src/math/mips/fabsf.c

+#if !defined(__mips_soft_float) && defined(__mips_abs2008)
+
+#include <math.h>
+
+float fabsf(float x)
+{
+	float r;
+	__asm__("abs.s %0,%1" : "=f"(r) : "f"(x));
+	return r;
+}
+
+#else
+
+#include "../fabsf.c"
+
+#endif

src/math/mips/sqrt.c

+#if !defined(__mips_soft_float) && __mips >= 3
+
+#include <math.h>
+
+double sqrt(double x)
+{
+	double r;
+	__asm__("sqrt.d %0,%1" : "=f"(r) : "f"(x));
+	return r;
+}
+
+#else
+
+#include "../sqrt.c"
+
+#endif

src/math/mips/sqrtf.c

+#if !defined(__mips_soft_float) && __mips >= 2
+
+#include <math.h>
+
+float sqrtf(float x)
+{
+	float r;
+	__asm__("sqrt.s %0,%1" : "=f"(r) : "f"(x));
+	return r;
+}
+
+#else
+
+#include "../sqrtf.c"
+
+#endif