Large brace-block initialisation makes CC Mode slow: Fix.

Large brace-block initialisation makes CC Mode slow: Fix.
Tidy up and accelerate c-in-literal, etc. by using the c-parse-state
routines.  Limit backward searching in c-font-lock-enclosing.decl.

cc-engine.el (c-state-pp-to-literal): Return the pp-state and literal
type in addition to the limits.
(c-state-safe-place): New defun, extracted from c-state-literal-at.
(c-state-literal-at): Use the above new defun.
(c-slow-in-literal, c-fast-in-literal): Removed.
(c-in-literal, c-literal-limits): Amended to use c-state-pp-to-literal.

cc-fonts.el (c-font-lock-enclosing-decls): Check for being in a literal.
Add a limit for backward searching.

cc-mode.el (awk-mode): Don't alias c-in-literal to c-slow-in-literal.