Swift package manifest decoding error

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We have three packages that consistently fail analysis

[ WARNING ] App.AppError.noValidVersions(Optional(AD2D160F-E6C7-42B2-B76B-8CD71AEEFF7B), "https://github.com/maparoni/GeoJSONKit-Turf.git") [component: analyze]
[ WARNING ] App.AppError.noValidVersions(Optional(A8DA9C80-6C44-4538-A99B-35909789FF79), "https://github.com/thepotatoking55/CGLFW3.git") [component: analyze]
[ WARNING ] App.AppError.noValidVersions(Optional(7D04578E-BFF3-4C89-8676-A2FF90365B04), "https://github.com/compnerd/swift-firebase.git") [component: analyze]

Starting with the first one, we fail version detection, because the package manifest contains .custom("xros", versionString: "1.0"), which we fail to decode:

DecodingError.dataCorrupted: Data was corrupted. Path: platformName. Debug description: invalid rawValue: xros

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The second package fails with

 50 | #endif
 51 |
 52 | let package = Package(
    |               `- error: the compiler is unable to type-check this expression in reasonable time; try breaking up the expression into distinct sub-expressions
 53 |     name: "CGLFW3",
 54 |     products: [
error: invalid manifests at [<AbsolutePath:"/Users/sas/Projects/SPI/spi-server/SPI-checkouts/github.com-thepotatoking55-cglfw3">]

There's no saving this but we should explore a fix that avoids triggering a critical error each time it comes around.

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Finally, we have

/Users/sas/Projects/SPI/spi-server/SPI-checkouts/github.com-compnerd-swift-firebase/Package.swift:5:8: error: no such module 'WinSDK'
  3 | import PackageDescription
  4 | import Foundation
  5 | import WinSDK
    |        `- error: no such module 'WinSDK'
  6 |
  7 | let swiftc = "swiftc.exe".withCString(encodedAs: UTF16.self) { pwszCompiler in
error: invalid manifests at [<AbsolutePath:"/Users/sas/Projects/SPI/spi-server/SPI-checkouts/github.com-compnerd-swift-firebase">]

Same applies here: we can't fix it.

On second thought, we may not want to suppress critical errors here just because we can't do anything about them. At least this way, we'd (more easily) see why a package isn't seeing version updates.

At least in the SwiftFirebase case, it's also easy to push a fix upstream by #ifdef guarding the import.

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I've proposed a fix for SwiftFirebase here: compnerd/swift-firebase#35