I'm compiling a program that requires plplot and, during its compilation defines the (very common) macro HAVE_CONFIG_H

Try this

$ cat test.c

#include "plplot.h"

$ gcc -DHAVE_CONFIG_H -I.  -I/usr/include/plplot  -c test.c

The compilation fails with

In file included from /usr/include/plplot/plplot.h:36:0,
                 from test.c:1:
/usr/include/plplot/plConfig.h:53:22: fatal error: config.h: No such file or directory
 #  include <config.h>

because plConfig.h contains 

#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

so this will fail if you don't have a config.h your include path, or worse, it will include the config.h or your project inside plplot.h (and you won't notice anything)

In Rawhide the file has this instead

#ifdef HAVE_CONFIG_H
#  include <plplot_config.h>
#endif

so it will always fail if you have HAVE_CONFIG_H defined.

C macros are ... funny...

May be solution to redefine the HAVE_CONFIG_H to HAVE_PLPLOT_CONFIG_H to avoid name colission?