Replace non-portable `basename | sed` with Awk in dejagnu launcher

ChangeLog

@@ -1,3 +1,10 @@
+2021-04-16  Jacob Bachmeyer  <jcb@gnu.org>
+
+	PR47382
+
+	* dejagnu (command): Use Awk instead of non-portable basename(1)
+	and a non-portable sed(1) pattern to initially set this variable.
+
 2021-04-15  Jacob Bachmeyer  <jcb@gnu.org>
 
 	PR47382

dejagnu

@@ -147,7 +147,20 @@ if $want_version ; then
 fi
 
 # Remove any leading autoconf platform prefix and the "dejagnu" prefix.
-command=`basename "$0" | sed -e 's/^.*-\?dejagnu-\?//'`
+# command=`basename "$0" | sed -e 's/^.*-\?dejagnu-\?//'`
+# The above simple solution is not portable, so we use Awk:
+command=`echo "$0" | awk 'BEGIN { FS = "/" }
+{   OFS = FS = "-"
+    $0 = $NF
+    for (i = 1; i <= NF; i++) if ($i ~ /dejagnu/) break;
+    for (j = 1; j <= (NF - i); j++) $j = $(j+i);
+    NF = j - 1
+    print }'`
+# Initially splitting on "/", then assigning the last field to the record
+# performs the role of basename.  Splitting on "-" and searching for a
+# field matching /dejagnu/ identifies the other prefixes, and the second
+# loop removes the "dejagnu" prefix and everything before it.  The record
+# is then truncated, printed, and thereby returned to the shell.
 
 while expr $# \> 0 > /dev/null
 do