ISO C99 features and compatibility

[Matthew Backes <mbackes@symas.com>]

We've recently stopped pretending to support building slapd with a  
K&R C compiler; it makes some sense to apply that to the libraries as  
well.  They are designed to be build-able in more places but it makes  
sense to require at least an ANSI C, considering the amount header  
cleanup we could do.

I'm also interested in potentially requiring some ISO C99 features;  
in particular variadic macros are very very attractive.  In addition  
to simplifying internal macro design, it allows for a great deal of  
cleanup and more flexibile macro use in the rest of OpenLDAP.

Consider Debug() and Statslog(); currently they are mostly the same,  
with the idea that Statslog takes two extra dedicated args (for  
connid and opid), and that Statslog() should appear even in a non- 
LDAP_DEBUG build.  As it sits, they don't share code and are  
implemented separately.  Worse, we have lots of

	Debug( LDAP_DEBUG_FOO, "foo\n", 0, 0, 0 );

Where the 0's should not be necessary.  Consider the case of adding a  
new compile-optional logging type; one currently needs to extend the  
macros for Debug() and Statslog() separately, and maintain large and  
separate ifdef trees for each build-option permutation.  A more  
elegant solution involves using a set of common macros to implement  
Debug and Statslog internally, but without variadic macros there must  
be separate implementations for each argument count, which defeats  
the purpose of unifying them in the first place.

Or we could preprocess all of the .c with m4...

But really, it seems reasonable to borrow a few features from a  
standard from 1999.  Is anyone actively maintaining OpenLDAP on  
platforms with no C99ish compiler available?

Matthew Backes
Symas Corporation
mbackes@symas.com