getARMCPU and getLLVMArchSuffixForARM existed as very similar functions
in both ToolChain.cpp and Tools.cpp. Create a single implementation of
each in Tools.cpp, eliminate the duplicate and share via Tools.h.

Creates an 'arm' namespace in Tools.h to be used by any ARM-targetting tools.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@197153 91177308-0d34-0410-b5e6-96231b3b80d8