Maintain c-syntax-table-hwm when changing syntax-table text properties

Maintain c-syntax-table-hwm when changing syntax-table text properties

* lisp/progmodes/cc-defs.el: (c-syntax-table-hwm): Move the defvar to here
from cc-mode.el, since the variable is needed at compile time in
c-emacs-features.
(c-min-property-position): New macro.
(c-put-char-property, c-clear-char-property, c-clear-char-properties)
(c-clear-char-property-with-value-function)
(c-clear-char-property-with-value-on-char-function)
(c-put-char-properties-on-char): Adjust c-syntax-table-hwm appropriately when
syntax-table text properties are changed.

* lisp/progmodes/cc-engine.el (c-truncate-lit-pos-cache): Remove the now
unneeded setting of c-syntax-table-hwm, and the unneeded declaration of
c-syntax-table-hwm.