Pass -explicit-target-dependency-import-check error when building swift-syntax

This should catch missing imports such as swiftlang#3195

Author: ahoppen

.github/workflows/pull_request.yml

@@ -19,6 +19,8 @@ jobs:
     uses: swiftlang/github-workflows/.github/workflows/swift_package_test.yml@main
     with:
       enable_wasm_sdk_build: true
+      linux_build_command: "swift test --explicit-target-dependency-import-check error"
+      windows_build_command: "Invoke-Program swift test --explicit-target-dependency-import-check error"
   soundness:
     name: Soundness
     uses: swiftlang/github-workflows/.github/workflows/soundness.yml@main

SwiftSyntaxDevUtils/Sources/swift-syntax-dev-utils/common/SwiftPMBuilder.swift

@@ -92,6 +92,7 @@ struct SwiftPMBuilder {
     if warningsAsErrors {
       args += ["-Xswiftc", "-warnings-as-errors"]
     }
+    args += ["--explicit-target-dependency-import-check", "error"]
 
     if release {
       args += ["--configuration", "release"]