vlib/math: Add a pure V backend for vlib/math (#11267)

vlib/math/exp.c.v

@@ -0,0 +1,17 @@
+module math
+
+fn C.exp(x f64) f64
+
+fn C.exp2(x f64) f64
+
+// exp calculates exponent of the number (math.pow(math.E, x)).
+[inline]
+pub fn exp(x f64) f64 {
+	return C.exp(x)
+}
+
+// exp2 returns the base-2 exponential function of a (math.pow(2, x)).
+[inline]
+pub fn exp2(x f64) f64 {
+	return C.exp2(x)
+}