Suppress warnings from dependencies with Swift Package Manager

With Swift Tools Version 5 you may define compiler flags in the package file (see https://docs.swift.org/package-manager/PackageDescription/PackageDescription.html#swiftsetting). Here is an example for a Package.swift which suppresses compiler warnings during build:

// swift-tools-version:5.0

import PackageDescription

let package = Package(
    name: "Antlr4",
    products: [
        .library(
            name: "Antlr4",
            targets: ["Antlr4"]),
    ],
    targets: [
        .target(
            name: "Antlr4",
            dependencies: [],
            swiftSettings: [
                .unsafeFlags(["-suppress-warnings"]),
            ]),
        .testTarget(
            name: "Antlr4Tests",
            dependencies: ["Antlr4"]),
    ]
)

To suppress warnings only in foreign code you should split the code into two packages.

For Objective-C modules, you can use the following to disable all warnings:

cSettings: [
   .unsafeFlags(["-w"])
]