Add support for patching config.guess interpreter line with CONFIG_SHELL

ChangeLog

@@ -2,6 +2,8 @@
 
 	* configure.ac: Change "dnl" comments that should appear in
 	configure to regular comments.
+	Add experimental support for propagating CONFIG_SHELL to the
+	config.sub and config.guess scripts in the source directory.
 
 2021-04-01  Jacob Bachmeyer  <jcb@gnu.org>
 

configure.ac

@@ -42,5 +42,25 @@ fi
 AC_SUBST(DEJAGNU)
 # Makefile.am arranges for DEJAGNU to be exported in the environment.
 
+# Patch interpreter lines in config.* scripts to reference CONFIG_SHELL.
+# Normally configure ensures that these scripts are run using CONFIG_SHELL
+# and their interpreter lines are ignored, but DejaGnu also installs
+# config.guess and the framework invokes it at runtime.
+if test x"$SHELL" != x/bin/sh
+then
+  AC_CONFIG_COMMANDS([scriptpatch],[
+    for file in config.guess config.sub
+    do
+      f=${ac_srcdir}/${file}
+      sed -e '1s,^@%:@!.*$,@%:@! '"${SHELL}", $f > ${f}.new
+      if test `awk 'END {print NR}' $f` != `awk 'END {print NR}' ${f}.new`
+      then
+	AC_MSG_ERROR([patching script for local shell changed line count!])
+      fi
+      mv -f ${f}.new $f
+    done
+], [SHELL=$SHELL])
+fi
+
 AC_CONFIG_FILES([Makefile])
 AC_OUTPUT