Use DECLSPEC_NORETURN and __attribute__((format (printf))) where appropriate in widl

[Vincent Béron]

Sorry for the whitespace noise, I tried to get rid of some constructs
(fprintf(proxy) and print_proxy() in a row, for example) and at the same
time tried to uniformize spacing around parenthesis, but maybe just
obscured what I really did.

Changelog:
Add a print_indent() function to print the spaces for the current indent
level.
Correct a couple incorrect format strings/too many args.
Use DECLSPEC_NORETURN where appropriate in widl.
Use __attribute__((format (printf))) where appropriate in widl.

Vincent