cmd/compile/internal/gc: convert fields of Type to bool

cmd/compile/internal/gc: convert fields of Type to bool

Convert some fields of struct Type in go.go from uint8 to bool.

This change passes go build -toolexec 'toolstash -cmp' -a std.

Change-Id: I0a6c53f8ee686839b5234010ee2de7ae3940d499
Reviewed-on: https://go-review.googlesource.com/14370
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>