Branch b1_6

b=16813
i=johann
i=panda

restore the ability to pass LD= through autoconf since x2 requires an
alternate LD program (x2ld).

build/autoconf/lustre-build-linux.m4

@@ -345,7 +345,7 @@ $2
 AC_DEFUN([LB_LINUX_COMPILE_IFELSE],
 [m4_ifvaln([$1], [LB_LINUX_CONFTEST([$1])])dnl
 rm -f build/conftest.o build/conftest.mod.c build/conftest.ko
-AS_IF([AC_TRY_COMMAND(cp conftest.c build && make [$2] CC="$CC" -f $PWD/build/Makefile LUSTRE_LINUX_CONFIG=$LINUX_CONFIG LINUXINCLUDE="$EXTRA_LNET_INCLUDE -I$LINUX/include -I$LINUX_OBJ/include -I$LINUX_OBJ/include2 -include include/linux/autoconf.h" -o tmp_include_depends -o scripts -o include/config/MARKER -C $LINUX_OBJ EXTRA_CFLAGS="-Werror-implicit-function-declaration $EXTRA_KCFLAGS" $ARCH_UM $MODULE_TARGET=$PWD/build) >/dev/null && AC_TRY_COMMAND([$3])],
+AS_IF([AC_TRY_COMMAND(cp conftest.c build && make [$2] LD="${LD:-ld}" CC="$CC" -f $PWD/build/Makefile LUSTRE_LINUX_CONFIG=$LINUX_CONFIG LINUXINCLUDE="$EXTRA_LNET_INCLUDE -I$LINUX/include -I$LINUX_OBJ/include -I$LINUX_OBJ/include2 -include include/linux/autoconf.h" -o tmp_include_depends -o scripts -o include/config/MARKER -C $LINUX_OBJ EXTRA_CFLAGS="-Werror-implicit-function-declaration $EXTRA_KCFLAGS" $ARCH_UM $MODULE_TARGET=$PWD/build) >/dev/null && AC_TRY_COMMAND([$3])],
 	[$4],
 	[_AC_MSG_LOG_CONFTEST
 m4_ifvaln([$5],[$5])dnl])dnl