AC_CHECK_HEADER question

[Dijk, J. van]

Dear all,

I can't imagine that I am the first to have this problem, but did
not manage to find a solution in the manual or on the Internet:
if I missed it, I apologize for that.

In our project, we are using the superlu code. On some systems, the headers are
present in <prefix>/include, on others in <prefix>/include/superlu. We therefore
#include the files without the superlu/ part, as in "#include "slu_util.h" and 
append
the directory <prefix>/superlu/ to the CPPFLAGS variable in our project.

How can I achieve this with autoconf? I mean: I know how to write a test like

AC_CHECK_HEADER(superlu/slu_util.h, foo, bar),

but how do I obtain (in 'foo') the path relative to which the file 
superlu/slu_util.h
was found? I was hoping that a variable, let's say 'header_location' is set, so
I can implement 'foo' as something like:

SUPERLU_CPPFLAGS="-I$header_location/superlu"

Is there such variable? Or can this be accomplished in a different way?

Your help is appreciated.

With kind regards,

Jan van Dijk.