Fix regression in std::random_device default constructor
When the default constructor was split out into a separate function (in
r261522) I accidentally made it call _M_init("mt19937") instead of
_M_init_pretr1("mt19937"). That means it will always throw an exception,
because "mt19937" isn't a valid token accepted by the _M_init function.
Restore the original behaviour by calling _M_init_pretr1("mt19937").
* include/bits/random.h (random_device) [!_GLIBCXX_USE_DEV_RANDOM]:
Fix default constructor to call correct function.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@265218 138bc75d-0d04-0410-961f-82ee72b054a4