Add cxx interop support to symbolgraph-extract

In order to extract symbol graphs for modules with transitive imports on
cxx modules we need parse headers in cxx mode using the option:
`-cxx-interoperability-mode=default`. This commit updates
`swift-symbolgraph-extract` to pass the option when there is a Cxx
module in the import graph.

This option is a new addition to `swift-symbolgraph-extract` added in
swiftlang/swift#73963.

Prior to this option's introduction, extracting the symbol graph for cxx
dependent modules would fail with an error similar to:
"unknown type name 'namespace'".

With this SwiftPM commit and `swift-symbolgraph-extract` _prior_ to
73963, users will instead see an argument parsing error like: "unknown
option -cxx-interoperability-mode".

With this change and `swift-symbolgraph-extract` 73963, the symbol graph
is extracted properly.

Author: rauhul

Sources/Commands/Utilities/SymbolGraphExtract.swift

@@ -13,7 +13,7 @@
 import ArgumentParser
 import Basics
 import PackageGraph
-import PackageModel
+@_spi(SwiftPMInternal) import PackageModel
 import SPMBuildCore
 
 #if USE_IMPL_ONLY_IMPORTS
@@ -82,7 +82,22 @@ public struct SymbolGraphExtract {
         if includeSPISymbols {
             commandLine += ["-include-spi-symbols"]
         }
-        
+
+        // If this target or any dependencies is is built with C++ interop
+        // enabled then swift-symbolgraph-extract must also enable C++ interop.
+        var cxxInterop = module.cxxInterop()
+        if !cxxInterop {
+            for module in try module.recursiveTargetDependencies() {
+                if module.cxxInterop() {
+                    cxxInterop = true
+                    break
+                }
+            }
+        }
+        if cxxInterop {
+            commandLine += ["-cxx-interoperability-mode=default"]
+        }
+
         let extensionBlockSymbolsFlag = emitExtensionBlockSymbols ? "-emit-extension-block-symbols" : "-omit-extension-block-symbols"
         if DriverSupport.checkSupportedFrontendFlags(flags: [extensionBlockSymbolsFlag.trimmingCharacters(in: ["-"])], toolchain: buildParameters.toolchain, fileSystem: fileSystem) {
             commandLine += [extensionBlockSymbolsFlag]
@@ -107,3 +122,14 @@ public struct SymbolGraphExtract {
         return try process.waitUntilExit()
     }
 }
+
+extension ResolvedModule {
+    func cxxInterop() -> Bool {
+        for setting in self.underlying.buildSettingsDescription {
+            if case .interoperabilityMode(.Cxx) = setting.kind {
+                return true
+            }
+        }
+        return false
+    }
+}