cmd/cgo: check for compiler errors in the C preamble

E.g., here's the new "go build" output:

$ go build misc/cgo/errors/issue8442.go
# command-line-arguments
could not determine kind of name for C.issue8442foo

gcc errors for preamble:
misc/cgo/errors/issue8442.go:11:19: error: unknown type name 'UNDEF'

Fixes #8442.

LGTM=iant
R=iant, alex.brainman
CC=golang-codereviews
https://golang.org/cl/129160043

2 files changed, 18 insertions, 0 deletions

diff --git a/misc/cgo/errors/issue8442.go b/misc/cgo/errors/issue8442.go
new file mode 100644
index 0000000000..45daf8e59e
--- /dev/null
+++ b/misc/cgo/errors/issue8442.go
@@ -0,0 +1,17 @@
+// Copyright 2014 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+// Issue 8442.  Cgo output unhelpful error messages for
+// invalid C preambles.
+
+/*
+void issue8442foo(UNDEF*); // ERROR HERE
+*/
+import "C"
+
+func main() {
+	C.issue8442foo(nil)
+}
diff --git a/misc/cgo/errors/test.bash b/misc/cgo/errors/test.bash
index e5bf47a0dd..c96264389c 100755
--- a/misc/cgo/errors/test.bash
+++ b/misc/cgo/errors/test.bash
@@ -28,6 +28,7 @@ check err1.go
 check err2.go
 check err3.go
 check issue7757.go
+check issue8442.go
 
 rm -rf errs _obj
 exit 0