SPMBuildCore: correct naming scheme for libraries on Windows
SPMBuildCore: correct naming scheme for libraries on Windows

Windows has a different naming scheme for libraries:
  lib<name>.lib: static libraries
  <name>.dll: shared libraries
  <name>.lib: import libraries for the shared library

Adjust the generated name for Windows targets.

abertelrud/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager,apple/swift-package-manager,apple/swift-package-manager