Fix terminal i/o issue in d_hlt

Due to the configuration of the tty, the getchar() call in d_hlt
returns nothing.  Work around this in the same way the SOC console
code does, by opening it on a separate unit, and reading from that
instead.  Without this fix, the code which looks for certain halt
cases and offers "continue or exit" just spins, printing its message
and getting no input.

em.c

@@ -6297,13 +6297,31 @@ d_hlt:  /* 000000 */
   if (bootarg) {
     printf("\nCPU halt, instruction #%u at %o/%o %s: %o %o ^%06o^\nA='%o/%d  B='%o/%d  L='%o/%d  X=%o/%d", gv.instcount, RPH, RPL, searchloadmap(gv.prevpc,' '), get16t(gv.prevpc), get16t(gv.prevpc+1), lights, getcrs16(A), getcrs16s(A), getcrs16(B), getcrs16s(B), getcrs32(A), getcrs32s(A), getcrs16(X), getcrs16s(X));
     while (1) {
+      int n;
+      static int ttydev;
+      ttydev = open("/dev/tty", O_RDWR, 0);
+      if (ttydev < 0) {
+        perror(" error opening /dev/tty");
+        fatal(NULL);
+      }
       printf("\nPress Enter to continue, h to halt... ");
-      utempa = getchar();
+      fflush(stdout);
+      utempa = ' ';
+      n = 0;
+      while (n == 0)
+        n = read(ttydev, &utempa, 1);
+/*    utempa = getchar(); */
       printf("\n");
       if (utempa == '\r' || utempa == '\n')
+      {
+        close(ttydev);
         goto fetch;
+      }
       if (utempa == 'h')
+      {
+        close(ttydev);
         break;
+      }
     }
   }
   fatal("CPU halt");