Correct the position of point in some line-up functions.

Correct the position of point in some line-up functions.
progmodes/cc-align.el (c-lineup-whitesmith-in-block, c-lineup-assignments)
(c-lineup-gcc-asm-reg ): take position of point at column 0 rather than
at a random place in the line.
doc/misc/cc-mode.texi (Custom Line-Up): State explicitly that point
starts at a random position in the line being indented.