Revert “Avoid some union buffered_input_event uses”

Revert “Avoid some union buffered_input_event uses”

Revert my commit 29a9fd4f4ba17822eca0f00c2037da3868bd874e
and the following commit 1ec0889e7b786d79351cee3ed4964d82295f059f.
This fixes a bug where ‘emacs -nw’ would sometimes freeze when Emacs is
configured with ‘--with-pgtk --enable-link-time-optimization
--disable-gc-mark-trace’ on GNU/Linux x86-64 (Bug#76729).
As it is not yet clear whether this freeze is due to an Emacs bug that
I introduced, or due to GCC bug 117423
<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117423>,
play it safe for now and revert to the previous state.

(cherry picked from commit 9415941a9c65b72a3bc20ae0ec1765f3c0ed657d)