Packaging: Support using Tools Support Core dylib

When Swift Package Manager used the SwiftBuild framework, it eventually
caused duplicate Swift Tools Support Core (TSC) duplicate symbols which
come from Swift Driver and Swift PM.

Swift PM depends on SwiftBuild, which depends on SwiftDriver, which
statically links TSC. Swift PM also has a statically linked dependency
on TSC.

The proper solution is to have SwiftDriver and SwiftPM both depend on
the TSC dynamic library when SwiftPM depends on the SwiftBuild framework,
which is determined by setting the SWIFTPM_SWBUILD_FRAMEWORK environment
variable.

rdar://144547608

Package.swift

@@ -10,6 +10,15 @@ if let deploymentTarget = ProcessInfo.processInfo.environment["SWIFTPM_MACOS_DEP
     macOSPlatform = .macOS(.v12)
 }
 
+let swiftToolsSupportCoreDep: [Target.Dependency]
+if ProcessInfo.processInfo.environment["SWIFTPM_SWBUILD_FRAMEWORK"] == nil {
+  swiftToolsSupportCoreDep = [
+    .product(name: "SwiftToolsSupport-auto", package: "swift-tools-support-core")
+  ]
+} else {
+  swiftToolsSupportCoreDep = []
+}
+
 let package = Package(
   name: "swift-driver",
   platforms: [
@@ -51,18 +60,16 @@ let package = Package(
       name: "SwiftDriver",
       dependencies: [
         "SwiftOptions",
-        .product(name: "SwiftToolsSupport-auto", package: "swift-tools-support-core"),
         "CSwiftScan",
-      ],
+      ] + swiftToolsSupportCoreDep,
       exclude: ["CMakeLists.txt"]),
 
     /// The execution library.
     .target(
       name: "SwiftDriverExecution",
       dependencies: [
         "SwiftDriver",
-        .product(name: "SwiftToolsSupport-auto", package: "swift-tools-support-core")
-      ],
+      ] + swiftToolsSupportCoreDep,
       exclude: ["CMakeLists.txt"]),
 
     /// Driver tests.
@@ -76,8 +83,8 @@ let package = Package(
       dependencies: [
         "IncrementalTestFramework",
         "TestUtilities",
-        .product(name: "SwiftToolsSupport-auto", package: "swift-tools-support-core"),
-      ]),
+      ] + swiftToolsSupportCoreDep
+    ),
 
     .target(
       name: "IncrementalTestFramework",
@@ -100,9 +107,7 @@ let package = Package(
     /// The options library.
     .target(
       name: "SwiftOptions",
-      dependencies: [
-        .product(name: "SwiftToolsSupport-auto", package: "swift-tools-support-core"),
-      ],
+      dependencies: swiftToolsSupportCoreDep,
       exclude: ["CMakeLists.txt"]),
     .testTarget(
       name: "SwiftOptionsTests",
@@ -120,8 +125,7 @@ let package = Package(
       dependencies: [
         "SwiftOptions",
         .product(name: "ArgumentParser", package: "swift-argument-parser"),
-        .product(name: "SwiftToolsSupport-auto", package: "swift-tools-support-core"),
-      ],
+      ] + swiftToolsSupportCoreDep,
       exclude: ["CMakeLists.txt"]),
 
     /// Build SDK Interfaces tool executable.