Remove automatic search for local Expect executable in DejaGnu testsuite

This search supported the old Cygnus tree layout, which has been obsolete
for a very long time.  Anyone still wanting to use a newly-built Expect
to run DejaGnu tests can do so by passing EXPECT explicitly on the runtest
command line (to use the new Expect only for the library unit tests) or in
the environment (which will also cause the runtest launcher script to use
it to run the framework).  Passing EXPECT in the environment can also be
achieved by setting EXPECT on the "make check" command line.

This remediates the test failures in PR47385 but does not address the
underlying root causes, which will be fixed in the 1.6.4 development phase.

ChangeLog

@@ -1,3 +1,10 @@
+2021-03-26  Jacob Bachmeyer  <jcb@gnu.org>
+
+	PR47385
+
+	* testsuite/lib/runtest.exp: Remove support for automatically
+	locating an Expect executable in the old Cygnus tree layout.
+
 2021-03-25  Jacob Bachmeyer  <jcb@gnu.org>
 
 	PR47382

NEWS

@@ -53,6 +53,10 @@ Changes since 1.6.2:
     The Tcl namespace ::dejagnu and all child namespaces are entirely
     internal and should not be mentioned in testsuite code.  Its contents
     are subject to change without notice, even on point releases.
+21. The DejaGnu testsuite no longer searches for a nearby Expect executable
+    in the location where it would have been located in the old Cygnus tree
+    layout.  If you want to use a special Expect other than the system
+    Expect, specify EXPECT=/name/of/expect to "runtest" or "make check".
 
 Changes since 1.6.1:
 

testsuite/lib/runtest.exp

@@ -1,4 +1,4 @@
-# Copyright (C) 1992-2016, 2018, 2020 Free Software Foundation, Inc.
+# Copyright (C) 1992-2016, 2018, 2020, 2021 Free Software Foundation, Inc.
 #
 # This file is part of DejaGnu.
 #
@@ -23,7 +23,11 @@ if { ![info exists RUNTEST] } {
 }
 
 if { ![info exists EXPECT] } {
-    set EXPECT [findfile $base_dir/../../expect/expect $base_dir/../../expect/expect expect]
+    if { [info exists ::env(EXPECT)] } {
+	set EXPECT $::env(EXPECT)
+    } else {
+	set EXPECT expect
+    }
     verbose "EXPECT defaulting to $EXPECT" 2
 }