Enable the static Linux SDK build

Helps keep the codebase free of unintentional Glibc-isms. There are also some interesting testing use cases enabled by building Swift Build using the static SDK.

Author: jakepetroules

.github/workflows/pull_request.yml

@@ -19,6 +19,8 @@ jobs:
       linux_swift_versions: '["nightly-main", "nightly-6.2"]'
       windows_swift_versions: '["nightly-main"]'
       windows_build_command: 'swift test --no-parallel'
+      enable_linux_static_sdk_build: true
+      linux_static_sdk_build_command: LLBUILD_STATIC_LINK=1 swift build
   cmake-smoke-test:
     name: cmake-smoke-test
     uses: swiftlang/github-workflows/.github/workflows/swift_package_test.yml@main