Define TM_MULTILIB_CONFIG for ARM multilib

Define TM_MULTILIB_CONFIG for ARM multilib

TM_MULTILIB_CONFIG is not set in config.gcc when building with multilib
for arm targets, leading to config/arm/t-multilib not including any of
the files (t-aprofile and t-rmprofile) definining the architecture and
FPU to build multilib for. This patch fixes that by setting
TM_MULTILIB_CONFIG to with_multilib_list's value after it has been
checked. It also fix a trailing whitespace issue.

2017-05-08  Thomas Preud'homme  <thomas.preudhomme@arm.com>

    gcc/
    * config.gcc (arm*-*-*): Set TM_MULTILIB_CONFIG from
    with_multilib_list after it has been checked.

From-SVN: r247741