debug/dwarf: formStrp uses a 64-bit value for 64-bit DWARF

No test as the only system I know that uses 64-bit DWARF is AIX.

Backport of https://golang.org/cl/84379, which will be in Go 1.11.
Backporting now for AIX support in gccgo.

Change-Id: I559ef119056230fb600973ccc1f033b15f3d979e
Reviewed-on: https://go-review.googlesource.com/87296
Reviewed-by: Than McIntosh <thanm@google.com>
1 file changed