libm: Add nanf() and tgammaf() implementations.

Requested by b/3370708 to export these through RenderScript.

Change-Id: I1ae69f87a1ad4765b2dee8e4a6f2f3a6eb7c5ad4
diff --git a/libm/include/math.h b/libm/include/math.h
index 3b5660f..a86a16f 100644
--- a/libm/include/math.h
+++ b/libm/include/math.h
@@ -251,6 +251,7 @@
 double	logb(double);
 long	lrint(double);
 long	lround(double);
+double	nan(const char *) __pure2;
 double	nextafter(double, double);
 double	remainder(double, double);
 double	remquo(double, double, int *);
@@ -343,6 +344,7 @@
 float	erfcf(float);
 float	hypotf(float, float);
 float	lgammaf(float);
+float	tgammaf(float);
 
 float	acoshf(float);
 float	asinhf(float);
@@ -354,6 +356,7 @@
 long long llroundf(float);
 long	lrintf(float);
 long	lroundf(float);
+float	nanf(const char *) __pure2;
 float	nearbyintf(float);
 float	nextafterf(float, float);
 float	remainderf(float, float);