Fix test/tools/llvm-mca/AArch64/Exynos/direct-branch.s on Mac

It was failing as below. Adding a triple seems to help.

--
: 'RUN: at line 2';   /work/llvm.combined/build.release/bin/llvm-mca -march=aarch64 -mcpu=exynos-m1 -resource-pressure=false < /work/llvm.combined/llvm/test/tools/llvm-mca/AArch64/Exynos/direct-branch.s | /work/llvm.combined/build.release/bin/FileCheck /work/llvm.combined/llvm/test/tools/llvm-mca/AArch64/Exynos/direct-branch.s -check-prefixes=ALL,M1
: 'RUN: at line 3';   /work/llvm.combined/build.release/bin/llvm-mca -march=aarch64 -mcpu=exynos-m3 -resource-pressure=false < /work/llvm.combined/llvm/test/tools/llvm-mca/AArch64/Exynos/direct-branch.s | /work/llvm.combined/build.release/bin/FileCheck /work/llvm.combined/llvm/test/tools/llvm-mca/AArch64/Exynos/direct-branch.s -check-prefixes=ALL,M3
--
Exit Code: 1

Command Output (stderr):
--
/work/llvm.combined/llvm/test/tools/llvm-mca/AArch64/Exynos/direct-branch.s:36:12: error: M1-NEXT: expected string not found in input
           ^
<stdin>:21:2: note: scanning from here
 1 0 0.25 b Ltmp0
 ^

--

llvm-svn: 348577