libc: introduce <envvars.h>

The new header envvars.h contains the names of commonly used
environment variables, such as $user, $ifs, $path and so on.

These defines are useful for Jehanne core applications that
use them to comunicate some values.

They are not strictly required, but having such defines we
can easily change the naming convention (from lowercase to uppercase).

sys/include/envvars.h

@@ -0,0 +1,44 @@
+/*
+ * This file is part of Jehanne.
+ *
+ * Copyright (C) 2017 Giacomo Tesio <giacomo@tesio.it>
+ *
+ * Jehanne is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 2 of the License.
+ *
+ * Jehanne is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Jehanne.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/* This file defines the names of a few environment variables shared
+ * among the userspace tools provided by Jehanne.
+ *
+ * It must not provide defines for variables used by commonly installed
+ * softwares, just the one used by the core tools, the one required
+ * to boot a minimal system.
+ */
+
+#define ENV_APID	"apid"
+#define ENV_USER	"user"
+#define ENV_HOME	"home"
+#define ENV_IFS		"ifs"
+#define ENV_PATH	"path"
+#define ENV_PID		"pid"
+#define ENV_PROMPT	"prompt"
+#define ENV_STATUS	"status"
+#define ENV_CDPATH	"cdpath"
+#define ENV_CPUTYPE	"cputype"
+#define ENV_SERVICE	"service"
+#define ENV_SYSNAME	"sysname"
+#define ENV_OBJTYPE	"objtype"
+
+#define ENV_WSYS	"wsys"
+
+extern	char*	jehanne_getenv(const char*);
+extern	int	jehanne_putenv(const char*, const char*);