50594.cc: For mingw-targets use only static libstdc++-version.

50594.cc: For mingw-targets use only static libstdc++-version.

	* testsuite/18_support/50594.cc: For mingw-targets use only static
	libstdc++-version.
	* testsuite/19_diagnostics/error_category/operators/equal.cc
	* testsuite/19_diagnostics/error_code/cons/1.cc
	* testsuite/19_diagnostics/error_code/operators/bool.cc
	* testsuite/19_diagnostics/error_code/operators/equal.cc
	* testsuite/19_diagnostics/error_code/operators/not_equal.cc
	* testsuite/19_diagnostics/error_condition/cons/1.cc
	* testsuite/19_diagnostics/error_condition/operators/bool.cc
	* testsuite/19_diagnostics/error_condition/operators/equal.cc
	* testsuite/19_diagnostics/error_condition/operators/not_equal.cc
	* testsuite/23_containers/set/requirements/exception/basic.cc
	* testsuite/26_numerics/headers/cmath/c99_classification_macros_c.cc
	* testsuite/lib/dg-options.exp (dg-additional-options): New option.

From-SVN: r197032