devel/cdecl: upgrade to 16.4.1

ChangeLog:
16.4:
Echoing commands short option
The short option for --echo-commands has been changed from -O to -E.

Number help
Help now includes what a "number" is.

Shell completion options
There are two new options: --commands/-K that prints cdecl's commands for the current language and --options/-O that prints cdecl's options. Both are intended to aid in writing shell completion functions for cdecl.

Shell completion functions
Bash and Zsh shell completion functions for cdecl are included under share and are installed as part of make install.

Improved error messages for predefined types
Improved error messages in cases involving a predefined type such as:

cdecl> explain int int8_t
cdecl> struct int8_t
In both cases, the error message printed now is:

error: "int8_t" is a predefined type starting in C99

16.4.1:
Fixed make install DESTDIR=...
Fixed make install of shell completion functions when setting DESTDIR on the command-line.

Better error message when expanding VA_* macros
Attempting to expand either VA_ARGS__ or VA_OPT now says that either is valid only in a macro definition.