cmd/cgo: do not use gcc -xc - to compile standard input

We have private reports of compilers that mishandle that.
Write to a temporary file instead.

Change-Id: I92e3cf4274b1a8048741e07fb52b8900c93b915e
Reviewed-on: https://go-review.googlesource.com/19616
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/cgo/util.go

@@ -8,6 +8,7 @@ import (
 	"bytes"
 	"fmt"
 	"go/token"
+	"io/ioutil"
 	"os"
 	"os/exec"
 )
@@ -16,6 +17,43 @@ import (
 // It returns the output to standard output and standard error.
 // ok indicates whether the command exited successfully.
 func run(stdin []byte, argv []string) (stdout, stderr []byte, ok bool) {
+	if i := find(argv, "-xc"); i >= 0 && argv[len(argv)-1] == "-" {
+		// Some compilers have trouble with standard input.
+		// Others have trouble with -xc.
+		// Avoid both problems by writing a file with a .c extension.
+		f, err := ioutil.TempFile("", "cgo-gcc-input-")
+		if err != nil {
+			fatalf("%s", err)
+		}
+		name := f.Name()
+		f.Close()
+		if err := ioutil.WriteFile(name+".c", stdin, 0666); err != nil {
+			os.Remove(name)
+			fatalf("%s", err)
+		}
+		defer os.Remove(name)
+		defer os.Remove(name + ".c")
+
+		// Build new argument list without -xc and trailing -.
+		new := append(argv[:i:i], argv[i+1:len(argv)-1]...)
+
+		// Since we are going to write the file to a temporary directory,
+		// we will need to add -I . explicitly to the command line:
+		// any #include "foo" before would have looked in the current
+		// directory as the directory "holding" standard input, but now
+		// the temporary directory holds the input.
+		// We've also run into compilers that reject "-I." but allow "-I", ".",
+		// so be sure to use two arguments.
+		// This matters mainly for people invoking cgo -godefs by hand.
+		new = append(new, "-I", ".")
+
+		// Finish argument list with path to C file.
+		new = append(new, name+".c")
+
+		argv = new
+		stdin = nil
+	}
+
 	p := exec.Command(argv[0], argv[1:]...)
 	p.Stdin = bytes.NewReader(stdin)
 	var bout, berr bytes.Buffer
@@ -30,6 +68,15 @@ func run(stdin []byte, argv []string) (stdout, stderr []byte, ok bool) {
 	return
 }
 
+func find(argv []string, target string) int {
+	for i, arg := range argv {
+		if arg == target {
+			return i
+		}
+	}
+	return -1
+}
+
 func lineno(pos token.Pos) string {
 	return fset.Position(pos).String()
 }