builder/picolib: add needed file for compiling math functions with error support.

Thanks to @aykevl for actually finding and providing this fix, I really just
reported the problem and tested the fix.

Signed-off-by: deadprogram <ron@hybridgroup.com>

testdata/math.go

@@ -39,6 +39,7 @@ func main() {
 		println("  remainder:", math.Remainder(n, n+0.2))
 		println("  sin:      ", math.Sin(n))
 		println("  sinh:     ", math.Sinh(n))
+		println("  sqrt:     ", float32(math.Sqrt(float64(n))))
 		println("  tan:      ", math.Tan(n))
 		println("  tanh:     ", math.Tanh(n))
 		println("  trunc:    ", math.Trunc(n))