gnu: openmpi: Modify configuration to reduce closure.

devel-headers are only for building MCA components, produce a large
closure and aren't normally packaged.  Only the affinity component of
mpi-ext is useful.

* gnu/packages/mpi.scm (openmpi)[arguments]: Don't configure
--with-devel-headers and --enable-mpi-ext=all.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

gnu/packages/mpi.scm

@@ -134,8 +134,7 @@ bind processes, and much more.")
     (arguments
      `(#:configure-flags `("--enable-builtin-atomics"
 
-                           "--enable-mpi-ext=all"
-                           "--with-devel-headers"
+                           "--enable-mpi-ext=affinity" ;cr doesn't work
                            "--enable-memchecker"
                            "--with-sge"
                            ,(string-append "--with-valgrind="