* config/abi/pre/gnu.ver (GLIBCXX_3.4.20): Correct regex_error export.
	(GLIBCXX_3.4.21): Export base object constructor for regex_error.
	* acinclude.m4 (libtool_VERSION): Bump.
	* configure: Regenerate.
	* testsuite/util/testsuite_abi.cc: Add GLIBCXX_3.4.21 version.
	* testsuite/28_regex/regex_error/base.cc: New.

From-SVN: r210290