Style fixes to `_libelftc.h`:
 * Keep function prototypes sorted by function name.
 * Use descriptive parameter names in function prototypes.
 * Use `__BEGIN_DECLS` and `__END_DECLS` to demarcate function
   prototypes.

Ticket:	#367

git-svn-id: https://elftoolchain.svn.sourceforge.net/svnroot/elftoolchain/trunk@2852 95820547-d848-0410-985e-9ae8fe0fa350