tests,arch-arm: Replaced X86 clang fast build for ARM_MESI_THREE
tests,arch-arm: Replaced X86 clang fast build for ARM_MESI_THREE

Given ARM_MESI_THREE_Level_HTM is a superset of ARM, it is logical to
compile it with clang and with 'fast' compiler optimizations when
checking for errors. This increases our test coverage

Change-Id: I320291cd543e5db8f543edd81facc91f3f52e17b
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/38315
Reviewed-by: Bobby R. Bruce <b9dba908ffb6c6d8ffe449cc88b3709c13c485c2@ucdavis.edu>
Maintainer: Bobby R. Bruce <b9dba908ffb6c6d8ffe449cc88b3709c13c485c2@ucdavis.edu>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

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