go.tools/go/types: fix float32 conversion

[griesemer]

gotype fails for:

package p
const x = float32(340282356779733661637539395458142568447)

with:

x.go:2:19: cannot convert 340282356779733661637539395458142568447 (untyped int constant)
to float32

Once this is fixed, we can re-enable float_lit2.go in the StdTest tests.

See also issue #8065.

[gopherbot]

Comment 1:

CL https://golang.org/cl/95580045 mentions this issue.

[griesemer]

Comment 2:

Status changed to Started.

[griesemer]

Comment 3:

This issue was closed by revision golang/tools@459aaad.

Status changed to Fixed.

[gopherbot]

Comment 4 by amrut.joshi:

This change broke Go1.2. math.big.Float32 is available only on 1.3. Is this intentional?

[griesemer]

Comment 5:

#4: https://golang.org/cl/105160043 should fix the build for 1.2 and 1.3.