clang-format: Add an option 'SpaceAfterCStyleCast'.

This permits to add a space after closing parenthesis of a C-style cast.
Defaults to false to preserve old behavior.

Fixes llvm.org/PR19982.

Before:
  (int)i;

After:
  (int) i;

Patch by Marek Kurdej.

llvm-svn: 217022