go/parser: report //go:build-derived Go version in ast.File.GoVersion

For #57001, compilers and others tools will need to understand that
a different Go version can be used in different files in a program,
according to the //go:build lines in those files.

Update go/parser to populate the new ast.File.GoVersion field.

This requires running the go/scanner in ParseComments mode
always and then implementing discarding of comments in the
parser instead of the scanner. The same work is done either way,
since the scanner was already preparing the comment result
and then looping. The loop has just moved into go/parser.

Also make the same changes to cmd/compile/internal/syntax,
both because they're necessary and to keep in sync with go/parser.

For #59033.

Change-Id: I7b867f5f9aaaccdca94af146b061d16d9a3fd07f
Reviewed-on: https://go-review.googlesource.com/c/go/+/476277
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>

0 files changed, 0 insertions, 0 deletions