can't build with system pcre / pcre_stack_guard not implemented

cmake checks for pcre_stack_guard:

CHECK_LIBRARY_EXISTS(pcre pcre_stack_guard "" HAVE_PCRE_STACK_GUARD)

this check always results in a Segmentation fault, since pcre_stack_guard should point to a function which checks if the stack is correct.

If the idea is, to detect stack problems, this has to be implemented by mariadb no matter if the bundled pcre or the external is used.

The message "system pcre is not found or unusable" doesn't tell much what was wrong here.