Add extraCPPFlags to BuildParameters
Add extraCPPFlags to BuildParameters

Currently the extra-cpp-flags specified in a destination.json file are not
passed through to clang. This is because the extra cpp flags are not being
encoded. This patch fixes that.

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