Use host_config_flag for other host libraries.

Pass the baseline host architecture when building
the other compatible host libraries.

See GNUTOOLS-13500

Change-Id: Ida41a7da2bc1fc492b65eaffb4518b90ae82ca06
Reviewed-on: https://eu-gerrit-1.euhpc.arm.com/c/dsg-gnu/Internal/gnu-devtools-for-arm/+/745162


Reviewed-by: Daniel Fellows <daniel.fellows@arm.com>
Tested-by: Service account - used by users in DSG GNU team <dgboter@arm.com>
Reviewed-by: Vaseeharan Vinayagamoorthy <vaseeharan.vinayagamoorthy@arm.com>
Reviewed-on: https://eu-gerrit-1.euhpc.arm.com/c/dsg-gnu/Internal/gnu-devtools-for-arm/+/758306


Tested-by: Daniel Fellows <daniel.fellows@arm.com>