Avoid unnecessary inclusion of <stdexcept> header

Avoid unnecessary inclusion of <stdexcept> header

This can greatly reduce the amount of preprocessed code that is included
by other headers, because <stdexcept> depends on <string> which is huge.

	* include/std/array: Do not include <stdexcept>.
	* include/std/optional: Include <exception> and
	<bits/exception_defines.h> instead of <stdexcept>.
	* testsuite/20_util/function_objects/searchers.cc: Include <cctype>
	for std::isalnum.
	* testsuite/20_util/tuple/cons/deduction.cc: Include <memory> for
	std::allocator.
	* testsuite/23_containers/map/erasure.cc: Include <string>.
	* testsuite/23_containers/unordered_map/erasure.cc: Likewise.

From-SVN: r272011