configure: simplify exit traps

This does the same thing and also fixes the trapping in
some (possibly broken) shells.

Suggested by Michael Kostylev.

Signed-off-by: Mans Rullgard <mans@mansr.com>
(cherry picked from commit 93bb9ff08e)

configure

@@ -1811,7 +1811,6 @@ tmpfile(){
 }
 
 trap 'rm -f -- $TMPFILES' EXIT
-trap exit HUP INT TERM
 
 tmpfile TMPC  .c
 tmpfile TMPE  $EXESUF