math: fix erf tests in directed rounding modes

erf has larger than 1 ULP errors in directed rounding modes,
increase the error threshold to 1.4 ULP in the test script.

Author: nsz-arm

math/test/runulp.sh

@@ -73,12 +73,14 @@ t pow  0x1.ffffffffff000p-1  0x1p0 x 0x1p50 0x1p52 50000
 t pow -0x1.ffffffffff000p-1 -0x1p0 x 0x1p50 0x1p52 50000
 
 L=1.0
+Ldir=0.9
 t erf  0 0xffff000000000000 10000
 t erf  0x1p-1022  0x1p-26   40000
 t erf  -0x1p-1022 -0x1p-26  40000
 t erf  0x1p-26    0x1p3     40000
 t erf  -0x1p-26  -0x1p3     40000
 t erf  0         inf        40000
+Ldir=0.5
 
 L=0.01
 t expf  0    0xffff0000    10000