base: Revert 9277177eccff and use getenv/setenv for UTC time

This patch reverts changeset 9277177eccff which does not do what it
was intended to do. In essence, we go back to implementing mkutctime
much like the non-standard timegm extension.

src/dev/sparc/dtod.cc

@@ -53,8 +53,7 @@ DumbTOD::DumbTOD(const Params *p)
     : BasicPioDevice(p, 0x08)
 {
     struct tm tm = p->time;
-    time_t local = mktime(&tm);
-    todTime = mktime(gmtime(&local));
+    todTime = mkutctime(&tm);
 
     DPRINTFN("Real-time clock set to %s\n", asctime(&tm));
     DPRINTFN("Real-time clock set to %d\n", todTime);