math: inf,nan,fmod for the JS backend (#11246)

vlib/math/bits.c.v

@@ -0,0 +1,12 @@
+module math
+
+// inf returns positive infinity if sign >= 0, negative infinity if sign < 0.
+pub fn inf(sign int) f64 {
+	v := if sign >= 0 { uvinf } else { uvneginf }
+	return f64_from_bits(v)
+}
+
+// nan returns an IEEE 754 ``not-a-number'' value.
+pub fn nan() f64 {
+	return f64_from_bits(uvnan)
+}