Improve lgammaf range for very small cases

The original cut for small arguments at |x|<2**-70 (copied from the
double version) produces that when computing nadj we get a subnormal
number for t*x and thus, the division of pi/subnormal will be INF and
the logarithm of it too, which is wrong as a result for lgammaf in this
range.
The proposed new limit seems to be safe and has been tested to
produce accurate results.
(Courtesy of Andreas Jung, ESA)

newlib/libm/math/erf_lgamma.c

@@ -168,7 +168,7 @@ static float zero=  0.0000000000e+00;
 	        *signgamp = -1;
 	    return one/(x-x);
 	}
-	if(ix<0x1c800000) {	/* |x|<2**-70, return -log(|x|) */
+	if(ix<0x30800000) {	/* |x|<2**-30, return -log(|x|) */
 	    if(hx<0) {
 	        *signgamp = -1;
 	        return -__ieee754_logf(-x);