Sys_var_keycache inherits from some variant of Sys_var_integer

Instances of Sys_var_keycache are initialized using the KEYCACHE_VAR macro,
which takes an offset within st_key_cache.
However, the Sys_var_integer CTOR treats the offset as if it was within
global_system_variables (hidden within some layers of macros and fuction
pointers)

The result is that we write arbitrary data to arbitrary locations in memory.
This all happens during static initialization of global objects,
i.e. before we have even entered the main() function.


Bug#12325449 TYPO IN CMAKE/DTRACE.CMAKE
Fix typo in dtrace.cmake