cmd/compile: check for missing function body earlier

Tested by fixedbugs/issue3705.go.

This removes a dependency on lineno
from near the backend.

Change-Id: I228bd0ad7295cf881b9bdeb0df9d18483fb96821
Reviewed-on: https://go-review.googlesource.com/38382
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/gc/noder.go

@@ -319,6 +319,10 @@ func (p *noder) funcDecl(fun *syntax.FuncDecl) *Node {
 
 	funcbody(f)
 
+	if f.Nbody.Len() == 0 && (pure_go || strings.HasPrefix(f.Func.Nname.Sym.Name, "init.")) {
+		yyerrorl(f.Pos, "missing function body for %q", f.Func.Nname.Sym.Name)
+	}
+
 	return f
 }
 

src/cmd/compile/internal/gc/pgen.go

@@ -12,7 +12,6 @@ import (
 	"cmd/internal/sys"
 	"fmt"
 	"sort"
-	"strings"
 )
 
 // "Portable" code generation.
@@ -278,11 +277,6 @@ func compile(fn *Node) {
 	dowidth(fn.Type)
 
 	if fn.Nbody.Len() == 0 {
-		if pure_go || strings.HasPrefix(fn.Func.Nname.Sym.Name, "init.") {
-			yyerror("missing function body for %q", fn.Func.Nname.Sym.Name)
-			return
-		}
-
 		emitptrargsmap()
 		return
 	}