Bring Back prefix support

We now have a team member who is interested in OpenRC on prefix, so I am
bringing it back to the main tree.

src/librc/librc.c

@@ -216,6 +216,7 @@ rc_sys_v2(void)
 		}
 		/* Now do detection */
 		__STRING_SWITCH(systype)
+		__STRING_CASE(RC_SYS_PREFIX)	{ return RC_SYS_PREFIX; }
 #ifdef __FreeBSD__
 		__STRING_CASE(RC_SYS_JAIL) { return RC_SYS_JAIL; }
 #endif /* __FreeBSD__ */
@@ -245,6 +246,10 @@ librc_hidden_def(rc_sys_v2)
 const char *
 rc_sys_v1(void)
 {
+#ifdef PREFIX
+	return RC_SYS_PREFIX;
+#else
+
 #ifdef __FreeBSD__
 	int jailed = 0;
 	size_t len = sizeof(jailed);
@@ -281,6 +286,7 @@ rc_sys_v1(void)
 #endif
 
 	return NULL;
+#endif /* PREFIX */
 }
 librc_hidden_def(rc_sys_v1)
 

src/librc/rc.h.in

@@ -280,6 +280,7 @@ bool rc_service_daemons_crashed(const char *);
 #define RC_SYS_JAIL    "JAIL"
 #define RC_SYS_OPENVZ  "OPENVZ"
 #define RC_SYS_LXC     "LXC"
+#define RC_SYS_PREFIX  "PREFIX"
 #define RC_SYS_UML     "UML"
 #define RC_SYS_VSERVER "VSERVER"
 #define RC_SYS_XEN0    "XEN0"