build: merge bootstrap changes from gnulib

* bootstrap: Update from gnulib.

diff --git a/bootstrap b/bootstrap
index 4be24b6..138239d 100755 (executable)
--- a/bootstrap
+++ b/bootstrap
@@ -150,12 +150,18 @@ vc_ignore=auto
 
 # find_tool ENVVAR NAMES...
 # -------------------------
+# Search for a required program.  Use the value of ENVVAR, if set,
+# otherwise find the first of the NAMES that can be run (i.e.,
+# supports --version).  If found, set ENVVAR to the program name,
+# die otherwise.
 find_tool ()
 {
   # Find sha1sum, named gsha1sum on MacPorts.
   find_tool_envvar=$1
   shift
-  if eval test x"\$$find_tool_envvar" = x; then
+  find_tool_names=$@
+  eval "find_tool_res=\$$find_tool_envvar"
+  if test x"$find_tool_res" = x; then
     for i
     do
       if ($i --version </dev/null) >/dev/null 2>&1; then
@@ -163,16 +169,18 @@ find_tool ()
        break
       fi
     done
+  else
+    find_tool_error_prefix="\$$find_tool_envvar: "
   fi
   if test x"$find_tool_res" = x; then
-    echo >&2 "$0: $find_tool_name is required"
+    echo >&2 "$0: one of these is required: $find_tool_names"
     exit 1
   fi
   ($find_tool_res --version </dev/null) >/dev/null 2>&1 || {
-    echo >&2 "$0: cannot run $find_tool_res --version"
+    echo >&2 "$0: ${find_tool_error_prefix}cannot run $find_tool_res --version"
     exit 1
   }
-  eval "$find_tool_envvar=\"$find_tool_res\""
+  eval "$find_tool_envvar=\$find_tool_res"
   eval "export $find_tool_envvar"
 }
 
@@ -721,6 +729,10 @@ find "$m4_base" "$source_base" \
 
 # Reconfigure, getting other files.
 
+# Skip autoheader if it's not needed.
+grep '^[        ]*AC_CONFIG_HEADERS\>' configure.ac >/dev/null ||
+  AUTOHEADER=true
+
 for command in \
   libtool \
   "${ACLOCAL-aclocal} --force -I m4" \