Include assembly files in builtins library build

The CMake assembler build system ignores the .S assembly files in builtins
library build. This patch fixes the issue.

Patch by: Sumanth Gundapaneni

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@213684 91177308-0d34-0410-b5e6-96231b3b80d8
Fix incompatible assembly in ARM builtins library

Convert the CBNZ backward branch instruction to CMP and BNE
avoiding illegal backwards branch and making the assembly code
in synh-ops.h to be UAL compliant.

Patch by: Sumanth Gundapaneni

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@213685 91177308-0d34-0410-b5e6-96231b3b80d8