Pacify --enable-gcc-warnings

Pacify --enable-gcc-warnings

* src/charset.c (load_charset_map):
* src/coding.c (decode_coding_object):
* src/frame.c (make_frame):
* src/window.c (Frecenter):
Mark locals with UNINIT to silence false alarms from
-Wmaybe-uninitialized.
* src/lisp.h (SYMBOL_ALIAS, SYMBOL_BLV, SYMBOL_FWD)
(SET_SYMBOL_ALIAS, SET_SYMBOL_BLV, SET_SYMBOL_FWD):
Check and assume that values are nonnull.  This pacifies
-Wmaybe-uninitialized in Fmake_variable_buffer_local and
Fmake_local_variable.