lib/libm/wf_tgamma: Fix tgammaf handling of -inf, should return nan.

lib/libm/wf_tgamma.c

@@ -35,6 +35,10 @@
 {
         float y;
 	int local_signgam;
+	if (!isfinite(x)) {
+	  /* special cases: tgammaf(nan)=nan, tgammaf(inf)=inf, tgammaf(-inf)=nan */
+	  return x + INFINITY;
+	}
 	y = expf(__ieee754_lgammaf_r(x,&local_signgam));
 	if (local_signgam < 0) y = -y;
 #ifdef _IEEE_LIBM