Wait for EOF after quitting the emulator.

When shutting down the emulator and starting another, it's otherwise
possible for the first read from the new emulator to return an error
(EIO from the pty read in Expect).

build/simh/build.tcl

@@ -37,6 +37,7 @@ proc create_tape {file} {
 
 proc quit_emulator {} {
     respond "sim>" "q\r"
+    expect eof
 }
 
 proc initialize_comsat {} {

build/sims/build.tcl

@@ -43,6 +43,7 @@ proc create_tape {file} {
 
 proc quit_emulator {} {
     respond "sim>" "q\r"
+    expect eof
 }
 
 proc initialize_comsat {} {