[dev.cc] cmd/dist, lib9: make GOHOSTARCH, GOHOSTOS available to C programs

Needed for invoking a Go subprocess in the C code.
The Go tools live in $GOROOT/pkg/tool/$GOHOSTARCH_$GOHOSTOS.

Change-Id: I961b6b8a07de912de174b758b2fb87d77080546d
Reviewed-on: https://go-review.googlesource.com/3042
Reviewed-by: Ian Lance Taylor <iant@golang.org>

include/libc.h

@@ -292,6 +292,8 @@ extern	char*	getgoversion(void);
 extern	char*	getgoarm(void);
 extern	char*	getgo386(void);
 extern	char*	getgoextlinkenabled(void);
+extern	char*	getgohostos(void);
+extern	char*	getgohostarch(void);
 
 extern	char*	mktempdir(void);
 extern	void	removeall(char*);

src/cmd/dist/build.go

@@ -929,6 +929,8 @@ func install(dir string) {
 				compile = append(compile,
 					"-D", fmt.Sprintf("GOOS=%q", goos),
 					"-D", fmt.Sprintf("GOARCH=%q", goarch),
+					"-D", fmt.Sprintf("GOHOSTOS=%q", gohostos),
+					"-D", fmt.Sprintf("GOHOSTARCH=%q", gohostarch),
 					"-D", fmt.Sprintf("GOROOT=%q", goroot_final),
 					"-D", fmt.Sprintf("GOVERSION=%q", goversion),
 					"-D", fmt.Sprintf("GOARM=%q", goarm),

src/lib9/goos.c

@@ -52,8 +52,20 @@ getgo386(void)
 	return defgetenv("GO386", GO386);
 }
 
-char *
+char*
 getgoextlinkenabled(void)
 {
 	return GO_EXTLINK_ENABLED;
 }
+
+char*
+getgohostarch(void)
+{
+	return GOHOSTARCH;
+}
+
+char*
+getgohostos(void)
+{
+	return GOHOSTOS;
+}