Add missing dependency for LLVM 10 CMake builds

The dependency is not needed for x86_64 builds, but is for arm
builds. I stumpled upon it during my experiments to build a SwiftShader
Vulkan driver suitable for offline compilation of compute programs.

Change-Id: I64914cd069a34fbf827acf3ea7e62eddea2f701e
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/55929
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Elias Naur <mail@eliasnaur.com>
Commit-Queue: Elias Naur <mail@eliasnaur.com>
diff --git a/third_party/llvm-10.0/CMakeLists.txt b/third_party/llvm-10.0/CMakeLists.txt
index 0124ffe..96141e9 100644
--- a/third_party/llvm-10.0/CMakeLists.txt
+++ b/third_party/llvm-10.0/CMakeLists.txt
@@ -753,6 +753,7 @@
     ${LLVM_DIR}/lib/Transforms/Scalar/LoopUnrollPass.cpp
     ${LLVM_DIR}/lib/Transforms/Scalar/LoopUnswitch.cpp
     ${LLVM_DIR}/lib/Transforms/Scalar/LoopVersioningLICM.cpp
+    ${LLVM_DIR}/lib/Transforms/Scalar/LowerAtomic.cpp
     ${LLVM_DIR}/lib/Transforms/Scalar/LowerConstantIntrinsics.cpp
     ${LLVM_DIR}/lib/Transforms/Scalar/LowerExpectIntrinsic.cpp
     ${LLVM_DIR}/lib/Transforms/Scalar/LowerMatrixIntrinsics.cpp