Separating ARM/AArch64 Compiler-RT tests

Makes sure ARM bots don't run AArch64 and vice-versa, since not all
AArch64 systems can run AArch32 and no ARM hardware can run AArch64.

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@219304 91177308-0d34-0410-b5e6-96231b3b80d8