build: enable building X10 support with SPM

Enable building the Swift interfaces for X10 with SPM.  This effectively
hard-enables X10 support in TensorFlow as SPM does not provide
configuration.

In order to accomplish this, we need to create symbolic links to sources
in order to merge the `x10` sources into the TensorFlow module.  It is
not possible to simply move the sources to reflect this structure due to
out-of-tree use cases.

Author: compnerd

Package.swift

@@ -50,6 +50,10 @@ let package = Package(
         "PythonKit",
         "CTensorFlow",
         .product(name: "Numerics", package: "swift-numerics"),
+      ],
+      swiftSettings: [
+        .define("USING_X10_BACKEND"),
+        .define("DEFAULT_BACKEND_EAGER"),
       ]),
     .target(
       name: "Experimental",

Sources/TensorFlow/X10/APIs/CrossReplicaSum.swift

@@ -0,0 +1 @@
+../../../x10/swift_bindings/apis/CrossReplicaSum.swift

Sources/TensorFlow/X10/APIs/DeviceScope.swift

@@ -0,0 +1 @@
+../../../x10/swift_bindings/apis/DeviceScope.swift

Sources/TensorFlow/X10/APIs/RawOpsManual.swift

@@ -0,0 +1 @@
+../../../x10/swift_bindings/apis/RawOpsManual.swift

Sources/TensorFlow/X10/Device.swift

@@ -0,0 +1 @@
+../../x10/swift_bindings/Device.swift

Sources/TensorFlow/X10/RawOpsXLAGenerated.swift

@@ -0,0 +1 @@
+../../x10/swift_bindings/RawOpsXLAGenerated.swift

Sources/TensorFlow/X10/XLAScalarType.swift

@@ -0,0 +1 @@
+../../x10/swift_bindings/XLAScalarType.swift

Sources/TensorFlow/X10/XLATensor.swift

@@ -0,0 +1 @@
+../../x10/swift_bindings/XLATensor.swift