os: implement and smoketest os.Unsetenv

src/syscall/syscall_libc.go

@@ -142,6 +142,15 @@ func Setenv(key, val string) (err error) {
 	return
 }
 
+func Unsetenv(key string) (err error) {
+	keydata := cstring(key)
+	errCode := libc_unsetenv(&keydata[0])
+	if errCode != 0 {
+		err = getErrno()
+	}
+	return
+}
+
 func Mmap(fd int, offset int64, length int, prot int, flags int) (data []byte, err error) {
 	addr := libc_mmap(nil, uintptr(length), int32(prot), int32(flags), int32(fd), uintptr(offset))
 	if addr == unsafe.Pointer(^uintptr(0)) {
@@ -206,6 +215,10 @@ func libc_getenv(name *byte) *byte
 //export setenv
 func libc_setenv(name *byte, val *byte, replace int32) int32
 
+// int unsetenv(const char *name);
+//export unsetenv
+func libc_unsetenv(name *byte) int32
+
 // ssize_t read(int fd, void *buf, size_t count);
 //export read
 func libc_read(fd int32, buf *byte, count uint) int

src/syscall/syscall_nonhosted.go

@@ -72,6 +72,11 @@ func Setenv(key, val string) (err error) {
 	return ENOSYS
 }
 
+func Unsetenv(key string) (err error) {
+	// stub for now
+	return ENOSYS
+}
+
 func Environ() []string {
 	env := runtime_envs()
 	envCopy := make([]string, len(env))