To avoid needing to export a new symbol from the library (for now) the
new member function uses __attribute__((always_inline)).

libstdc++-v3/ChangeLog:

	* include/std/ostream (operator<<(const volatile void*)):
	Add new overload, as per P1147R1.
	* testsuite/27_io/basic_ostream/inserters_other/char/volatile_ptr.cc:
	New test.

Tested powerpc64le-linux. Committed to trunk.