Add autoconf macro to test for OpenMP collapse statement

[Erik Schnetter]

Keyword:

[Erik Schnetter]

It turns out that it would be difficult to create an actual autoconf test, since the symptoms are bad behaviour at run time. Instead, we should check the compiler vendor or version

I checked, and #defining collapse(N) should work fine.

[Roland Haas]

Patch looks ok. One comment: maybe we want to add a define for COLLAPSE (uppercase) as well as collapse for the Fortran case to provide some case insensitivity (assuming that no one spells collapse as "CoLllaSE" in Fortran even though they migh).

[Erik Schnetter]

Added upper-case version. Applied.