Drop worthless font zeroing

BSS is initialized to zero.  Explicitly zeroing it again wastes time and
space.
Store weapon_name as const char*
Mark gauges variables const
Add -Werror=format-security to build
Switch gr_printf(x,y,"%s",s) to gr_string(x,y,s)
Simplify setup of thief/buddy messages
Avoid unnecessary lookups in fix_sincos
Always use 64-bit math in vm_vec_dotprod
Always use 64-bit math in vm_vec_dot3
Remove fix.h