build: move GOOS, GOARCH, GOROOT lookup into central library.

bake default values in during build.

R=r
CC=golang-dev
https://golang.org/cl/186173

src/cmd/gc/lex.c

@@ -223,8 +223,8 @@ findpkg(Strlit *name)
 	Idir *p;
 
 	if(goroot == nil) {
-		goroot = getenv("GOROOT");
-		goos = getenv("GOOS");
+		goroot = getgoroot();
+		goos = getgoos();
 		goarch = thestring;
 	}
 

src/cmd/ld/lib.c

@@ -720,21 +720,9 @@ mywhatsys(void)
 {
 	char *s;
 
-	goroot = getenv("GOROOT");
-	goos = getenv("GOOS");
-
-	if(goroot == nil) {
-		s = getenv("HOME");
-		if(s == nil)
-			s = "/home/ken";
-		goroot = mal(strlen(s) + 10);
-		strcpy(goroot, s);
-		strcat(goroot, "/go");
-	}
+	goroot = getgoroot();
+	goos = getgoos();
 	goarch = thestring;	// ignore $GOARCH - we know who we are
-	if(goos == nil) {
-		goos = "linux";
-	}
 }
 
 int

src/lib9/Makefile

@@ -69,6 +69,7 @@ LIB9OFILES=\
 	getenv.$O\
 	getfields.$O\
 	getwd.$O\
+	goos.$O\
 	main.$O\
 	nan.$O\
 	nulldir.$O\
@@ -115,6 +116,9 @@ $(LIB): $(OFILES)
 %.$O: utf/%.c
 	$(CC) -c $(CFLAGS) $<
 
+goos.$O: goos.c
+	$(CC) -c $(CFLAGS) -DGOOS='"$(GOOS)"' -DGOARCH='"$(GOARCH)"' -DGOROOT='"$(GOROOT)"' $<
+
 clean:
 	rm -f *.$O *.6 6.out $(LIB)
 

src/lib9/goos.c

@@ -0,0 +1,35 @@
+// Copyright 2010 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.
+
+#include <u.h>
+#include <libc.h>
+
+static char*
+defgetenv(char *name, char *def)
+{
+	char *p;
+	
+	p = getenv(name);
+	if(p == nil || p[0] == '\0')
+		p = def;
+	return p;
+}
+
+char*
+getgoos(void)
+{
+	return defgetenv("GOOS", GOOS);
+}
+
+char*
+getgoarch(void)
+{
+	return defgetenv("GOARCH", GOARCH);
+}
+
+char*
+getgoroot(void)
+{
+	return defgetenv("GOROOT", GOROOT);
+}