build_variables.bzl: make MPS_BACKEND_SRCS usable in BUCK (#13355)

Making the structure in this file mirror buck's worldview more closely
when it makes sense. #8268

Differential Revision:
[D80187449](https://our.internmc.facebook.com/intern/diff/D80187449)

Author: swolchok

backends/apple/mps/targets.bzl

@@ -3,6 +3,7 @@
 #  Provided subject to the LICENSE file in the top level directory.
 #
 
+load("@fbsource//xplat/executorch/build:build_variables.bzl", "MPS_BACKEND_BUCK_SRCS")
 load("@fbsource//xplat/executorch/build:runtime_wrapper.bzl", "runtime")
 
 def define_common_targets(is_xplat = False, platforms = []):
@@ -37,10 +38,7 @@ def define_common_targets(is_xplat = False, platforms = []):
             "runtime/*.h",
             "runtime/operations/*.h",
         ]),
-        "srcs": native.glob([
-            "runtime/*.mm",
-            "runtime/operations/*.mm",
-        ]),
+        "srcs": MPS_BACKEND_BUCK_SRCS,
         "visibility": [
             "//executorch/backends/apple/...",
             "//executorch/examples/...",

shim_et/xplat/executorch/build/build_variables.bzl

@@ -437,31 +437,33 @@ MPS_EXECUTOR_RUNNER_SRCS = [
     "extension/data_loader/file_data_loader.cpp",
 ]
 
-MPS_BACKEND_SRCS = [
-    "backends/apple/mps/runtime/MPSBackend.mm",
-    "backends/apple/mps/runtime/MPSCompiler.mm",
-    "backends/apple/mps/runtime/MPSDelegateHeader.mm",
-    "backends/apple/mps/runtime/MPSDevice.mm",
-    "backends/apple/mps/runtime/MPSExecutor.mm",
-    "backends/apple/mps/runtime/MPSGraphBuilder.mm",
-    "backends/apple/mps/runtime/MPSStream.mm",
-    "backends/apple/mps/runtime/operations/ActivationOps.mm",
-    "backends/apple/mps/runtime/operations/BinaryOps.mm",
-    "backends/apple/mps/runtime/operations/ClampOps.mm",
-    "backends/apple/mps/runtime/operations/ConstantOps.mm",
-    "backends/apple/mps/runtime/operations/ConvolutionOps.mm",
-    "backends/apple/mps/runtime/operations/IndexingOps.mm",
-    "backends/apple/mps/runtime/operations/LinearAlgebra.mm",
-    "backends/apple/mps/runtime/operations/NormalizationOps.mm",
-    "backends/apple/mps/runtime/operations/OperationUtils.mm",
-    "backends/apple/mps/runtime/operations/PadOps.mm",
-    "backends/apple/mps/runtime/operations/PoolingOps.mm",
-    "backends/apple/mps/runtime/operations/QuantDequant.mm",
-    "backends/apple/mps/runtime/operations/RangeOps.mm",
-    "backends/apple/mps/runtime/operations/ReduceOps.mm",
-    "backends/apple/mps/runtime/operations/ShapeOps.mm",
-    "backends/apple/mps/runtime/operations/UnaryOps.mm",
-]
+MPS_BACKEND_BUCK_SRCS = [
+    "runtime/MPSBackend.mm",
+    "runtime/MPSCompiler.mm",
+    "runtime/MPSDelegateHeader.mm",
+    "runtime/MPSDevice.mm",
+    "runtime/MPSExecutor.mm",
+    "runtime/MPSGraphBuilder.mm",
+    "runtime/MPSStream.mm",
+    "runtime/operations/ActivationOps.mm",
+    "runtime/operations/BinaryOps.mm",
+    "runtime/operations/ClampOps.mm",
+    "runtime/operations/ConstantOps.mm",
+    "runtime/operations/ConvolutionOps.mm",
+    "runtime/operations/IndexingOps.mm",
+    "runtime/operations/LinearAlgebra.mm",
+    "runtime/operations/NormalizationOps.mm",
+    "runtime/operations/OperationUtils.mm",
+    "runtime/operations/PadOps.mm",
+    "runtime/operations/PoolingOps.mm",
+    "runtime/operations/QuantDequant.mm",
+    "runtime/operations/RangeOps.mm",
+    "runtime/operations/ReduceOps.mm",
+    "runtime/operations/ShapeOps.mm",
+    "runtime/operations/UnaryOps.mm",
+]
+
+MPS_BACKEND_SRCS = ["backends/apple/mps/" + x for x in MPS_BACKEND_BUCK_SRCS]
 
 MPS_SCHEMA_SRCS = [
     "backends/apple/mps/serialization/schema.fbs",