run pkgConfig in gradle config for Kotlin/Native

build.gradle.kts

/**
 * Runs `pkg-config`:
 * https://github.com/JetBrains/kotlin-native/issues/1534#issuecomment-384894431
 */
fun runPkgConfig(
    vararg packageNames: String,
    cflags: Boolean = false,
    libs: Boolean = false): List<String> {
    val p = ProcessBuilder(*(listOfNotNull(
        "pkg-config",
        if (cflags) "--cflags" else null,
        if (libs) "--libs" else null
    ).toTypedArray() + packageNames)).run {
        // https://github.com/JetBrains/kotlin-native/issues/3484#issuecomment-544926683
        environment()["PKG_CONFIG_ALLOW_SYSTEM_LIBS"] = "1"
        start()
    }.also { it.waitFor(10, TimeUnit.SECONDS) }

    if (p.exitValue() != 0) {
        throw GradleException("Error executing pkg-config: ${p.errorStream.bufferedReader().readText()}")
    }

    return p.inputStream.bufferedReader().readText().split(" ").map{ it.trim() }
}

fun DefaultCInteropSettings.pkgConfig(
    vararg packageNames: String,
    cflags: Boolean = true,
    libs: Boolean = true) {
    if (cflags) {
        compilerOpts.addAll(runPkgConfig(*packageNames, cflags=true))
    }

    if (libs) {
        linkerOpts.addAll(runPkgConfig(*packageNames, libs=true))
    }
}