[ARM] Fix build break after 762f0b5463

The commit adds a unit test that uses the facilities of libLLVMCore
without adding it to link components. This causes failures with
the shared libraries builds.

This patch just adds the missing library to the link step.

llvm/unittests/Target/ARM/CMakeLists.txt

@@ -8,6 +8,7 @@ set(LLVM_LINK_COMPONENTS
   ARMDesc
   ARMInfo
   CodeGen
+  Core
   GlobalISel
   MC
   MIRParser