Revert "Use host_config_flag for other host libraries."

This reverts commit 52a0dbedeee7093bae346f5bc1ffaf12597b4546.

This is due to the isl library not accepting the host name for Arm64 Darwin.

GNUTOOLS-13500

Change-Id: I1ca133cb1453bfd55e17ce5eb6e98308079c7694
Reviewed-on: https://eu-gerrit-1.euhpc.arm.com/c/dsg-gnu/Internal/gnu-devtools-for-arm/+/759814


Tested-by: Daniel Fellows <daniel.fellows@arm.com>
Reviewed-by: Vaseeharan Vinayagamoorthy <vaseeharan.vinayagamoorthy@arm.com>
Reviewed-by: Daniel Fellows <daniel.fellows@arm.com>
Tested-by: Service account - used by users in DSG GNU team <dgboter@arm.com>