build: bootstrap: add a comment; generalize autoheader check

* bootstrap: Sync from gnulib and diff.

diff --git a/bootstrap b/bootstrap
index 97300b477f9901fd0069e389cf98e3998c893f8d..1729d42b0a393e56e3006a38c685f0e8b4911ab0 100755 (executable)
--- a/bootstrap
+++ b/bootstrap
@@ -71,6 +71,7 @@ gnulib_modules=
 gnulib_files=
 
 # A function to be called after everything else in this script.
+# Override it via your own definition in bootstrap.conf.
 bootstrap_epilogue() { :; }
 
 # The command to download all .po files for a specified domain into
@@ -733,7 +734,7 @@ find "$m4_base" "$source_base" \
 # Reconfigure, getting other files.
 
 # Skip autoheader if it's not needed.
-grep '^[        ]*AC_CONFIG_HEADERS\>' configure.ac >/dev/null ||
+grep -E '^[     ]*AC_CONFIG_HEADERS?\>' configure.ac >/dev/null ||
   AUTOHEADER=true
 
 for command in \