bug#15880: Compute C declarations for DEFSYMs automatically.

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Date: Tue, 12 Nov 2013 23:19:06 -0500
> Cc: 15880@debbugs.gnu.org
> 
> I'm wondering about one issue, tho: this creates a "big single file
> dependency", so addition/removal of a DEFSYM somewhere causes
> recompilation of all files.

How is that different from changing variables and functions exposed to
Lisp, and the dependency on globals.h?