don't build BTLs when using portals SHMEM. It breaks things :)

This commit was SVN r24678.

contrib/platform/portals4-shmem

@@ -1,5 +1,5 @@
 with_memory_manager=no
-enable_mca_no_build=carto,compress,crs,maffinity,paffinity,debugger,notifier,bml,btl,coll-hierarch,coll-sm,common-sm,mpool,pml-bfo,pml-csum,pml-dr,pml-ob1,osc-rdma,rcache,vprotocol
+enable_mca_no_build=carto,compress,crs,maffinity,paffinity,debugger,notifier,bml,btl,coll-hierarch,coll-sm,common-sm,mpool,pml-bfo,pml-csum,pml-dr,pml-ob1,osc-rdma,rcache,vprotocol,btl
 enable_contrib_no_build=libnbc,vt
 with_rte_support=no
 enable_heterogeneous=no