CC Mode: Fix bug in whitespace scanning functions

CC Mode: Fix bug in whitespace scanning functions

c-forward-sws and c-backward-sws were scanning over spaces and
linefeeds marked with the string-fence syntax-table text
property.  Fix this by (i) removing the WS text properties
c-in-sws and c-is-sws from characters when setting the
string-fence on them; (ii) checking the syntax of "space"
characters when scanning over them.

* lisp/progmodes/cc-defs.el (c-skip-ws-chars-forward)
c-skip-ws-chars-backward, c-put-string-fence): New macros.

* lisp/progmodes/cc-awk.el
(c-awk-set-string-regexp-syntax-table-properties): Use
c-put-string-fence.

* lisp/progmodes/cc-engine.el (c-beginning-of-statement-1):
Correct the determination of macro-start.
(c-forward-sws, c-backward-sws): Replace skip-chars-forward by
c-skip-ws-chars-forward and skip-chars-backward by
c-skip-ws-chars-backward.
(c-unmark-<>-around-region, c-after-change-unmark-ml-strings)
(c-propertize-ml-string-opener): Use c-put-string-fence.

* lisp/progmodes/cc-mode.el (c-put-syn-tab): Use
c-put-string-fence when appropriate.