usnic: add --with-usnic configure switch

If --with-usnic is specified and we can't build the usnic BTL, abort.
If --without-usnic is specified, gracefully skip building the usnic
BTL.  If neither is specified, do the OMPI-default behavior: try to
configure/build the usnic BTL, and if we can't, skip it.
    
Fixes CSCuq13889.

This commit was SVN r32349.

opal/mca/btl/usnic/configure.m4

@@ -6,7 +6,7 @@
 # Copyright (c) 2004-2005 The University of Tennessee and The University
 #                         of Tennessee Research Foundation.  All rights
 #                         reserved.
-# Copyright (c) 2004-2005 High Performance Computing Center Stuttgart, 
+# Copyright (c) 2004-2005 High Performance Computing Center Stuttgart,
 #                         University of Stuttgart.  All rights reserved.
 # Copyright (c) 2004-2005 The Regents of the University of California.
 #                         All rights reserved.
@@ -14,9 +14,9 @@
 #                         reserved.
 # Copyright (c) 2010-2014 Cisco Systems, Inc.  All rights reserved.
 # $COPYRIGHT$
-# 
+#
 # Additional copyrights may follow
-# 
+#
 # $HEADER$
 #
 
@@ -107,12 +107,26 @@ AC_DEFUN([MCA_opal_btl_usnic_POST_CONFIG], [
                    [test "$1" -eq 1 && test "X$enable_opal_btl_usnic_libnl3_utils" = "Xyes"])
 ])
 
-# MCA_btl_usnic_CONFIG([action-if-can-compile], 
+# MCA_btl_usnic_CONFIG([action-if-can-compile],
 #                      [action-if-cant-compile])
 # ------------------------------------------------
 AC_DEFUN([MCA_opal_btl_usnic_CONFIG],[
     AC_CONFIG_FILES([opal/mca/btl/usnic/Makefile])
 
+    AC_ARG_WITH([usnic],
+                [AS_HELP_STRING([--with-usnic],
+                                [If specified, cause an error if usNIC
+                                 support cannot be built])])
+
+    # If --without-usnic was specified, then gracefully exit.
+    # Otherwise, do the rest of the config.
+    AS_IF([test "x$with_usnic" = "xno"],
+          [AC_MSG_WARN([--without-usnic specified; skipping usnic BTL])
+           $2],
+          [OMPI_BTL_USNIC_DO_CONFIG($1, $2)])
+])
+
+AC_DEFUN([OMPI_BTL_USNIC_DO_CONFIG],[
     # see README.test for information about this scheme
     AC_ARG_ENABLE([ompi-btl-usnic-unit-tests],
                   [AS_HELP_STRING([--enable-ompi-btl-usnic-unit-tests],
@@ -192,7 +206,12 @@ AC_DEFUN([MCA_opal_btl_usnic_CONFIG],[
           [btl_usnic_WRAPPER_EXTRA_LDFLAGS="$btl_usnic_LDFLAGS"
            btl_usnic_WRAPPER_EXTRA_LIBS="$btl_usnic_LIBS"
            $1],
-          [$2])
+          [AS_IF([test "$with_usnic" = "yes"],
+                 [AC_MSG_WARN([--with-usnic specified, but usNIC support cannot be built])
+                  AC_MSG_ERROR([Cannot continue])],
+                 [$2])
+          ])
+
 
     # Substitute in the things needed to build USNIC
     AC_SUBST([btl_usnic_CPPFLAGS])