cmd/compile: handle pragmas immediately with -newparser=1

Instead of saving all pragmas and processing them after parsing is
finished, process them immediately during scanning like the current
lexer does.

This is a bit unfortunate because it means we can't use
syntax.ParseFile to concurrently parse files yet, but it fixes how we
report syntax errors in the presence of //line pragmas.

While here, add a bunch more gcCompat entries to syntax/parser.go to
get "go build -toolexec='toolstash -cmp' std cmd" passing. There are
still a few remaining cases only triggered building unit tests, but
this seems like a nice checkpoint.

Change-Id: Iaf3bbcf2849857a460496f31eea228e0c585ce13
Reviewed-on: https://go-review.googlesource.com/28226
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/cmd/compile/internal/syntax/nodes.go

@@ -10,6 +10,7 @@ package syntax
 type Node interface {
 	Line() uint32
 	aNode()
+	init(p *parser)
 }
 
 type node struct {
@@ -35,16 +36,10 @@ func (n *node) init(p *parser) {
 type File struct {
 	PkgName  *Name
 	DeclList []Decl
-	Pragmas  []Pragma
 	Lines    int
 	node
 }
 
-type Pragma struct {
-	Line int
-	Text string
-}
-
 // ----------------------------------------------------------------------------
 // Declarations
 
@@ -90,6 +85,7 @@ type (
 		Name    *Name
 		Type    *FuncType
 		Body    []Stmt // nil means no body (forward declaration)
+		Pragma  Pragma // TODO(mdempsky): Cleaner solution.
 		EndLine uint32 // TODO(mdempsky): Cleaner solution.
 		decl
 	}
@@ -130,7 +126,8 @@ type (
 	CompositeLit struct {
 		Type     Expr // nil means no literal type
 		ElemList []Expr
-		NKeys    int // number of elements with keys
+		NKeys    int    // number of elements with keys
+		EndLine  uint32 // TODO(mdempsky): Cleaner solution.
 		expr
 	}