Add the __ARM_ARCH_EXT_IDIV__ predefine. It is set to 1 if we have hardware divide in the mode that we are compiling in (depending on the target features), not defined if we don't. Should be compatible with the GCC conterpart. Also adding a -hwdiv option to overide the default behavior.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@193074 91177308-0d34-0410-b5e6-96231b3b80d8