PlatformMacOSX should be activated for lldb built to run on an iOS etc device

[jasonmolenda]

Summary

In the changes Jonas made in https://reviews.llvm.org/D117340 , a small oversight was that PlatformMacOSX (despite the name) is active for any native Darwin operating system, where lldb and the target process are running on the same system. This patch uses compile-time checks to return the appropriate OSType for the OS lldb is being compiled to, so the "host" platform will correctly be selected when lldb & the inferior are both running on that OS. And a small change to PlatformMacOSX::GetSupportedArchitectures which adds additional recognized triples when running on macOS but not other native Darwin systems.

When PlatformMacOSX is compiled on a non-Darwin system where we don't have these availability macros, we will continue to return macOS as the OSType, as we were before.

[JDevlieghere]

LGTM

lldb/source/Plugins/Platform/MacOSX/PlatformDarwin.h

lldb_private::Status FindBundleBinaryInExecSearchPaths(
       const lldb_private::ModuleSpec &module_spec,
       lldb_private::Process *process, lldb::ModuleSP &module_sp,
       const lldb_private::FileSpecList *module_search_paths_ptr,
       llvm::SmallVectorImpl<lldb::ModuleSP> *old_modules, bool *did_create_ptr);
 
   static std::string FindComponentInPath(llvm::StringRef path,
                                          llvm::StringRef component);
 
+  // The OSType where lldb is running.
+  static llvm::Triple::OSType GetHostOSType();
+
   std::string m_developer_directory;
   llvm::StringMap<std::string> m_sdk_path;
   std::mutex m_sdk_path_mutex;
 
 private:
   PlatformDarwin(const PlatformDarwin &) = delete;
   const PlatformDarwin &operator=(const PlatformDarwin &) = delete;
 };
 
 #endif // LLDB_SOURCE_PLUGINS_PLATFORM_MACOSX_PLATFORMDARWIN_H

lldb/source/Plugins/Platform/MacOSX/PlatformDarwin.cpp

FileSpec PlatformDarwin::GetCurrentToolchainDirectory() {
   return {};
 }
 
 FileSpec PlatformDarwin::GetCurrentCommandLineToolsDirectory() {
   if (FileSpec fspec = HostInfo::GetShlibDir())
     return FileSpec(FindComponentInPath(fspec.GetPath(), "CommandLineTools"));
   return {};
 }
+
+llvm::Triple::OSType PlatformDarwin::GetHostOSType() {
+#if !defined(__APPLE__)
+  return llvm::Triple::MacOSX;
+#else
+#if TARGET_OS_OSX
+  return llvm::Triple::MacOSX;
+#elif TARGET_OS_IOS
+  return llvm::Triple::IOS;
+#elif TARGET_OS_WATCH
+  return llvm::Triple::WatchOS;
+#elif TARGET_OS_TV
+  return llvm::Triple::TvOS;
+#elif TARGET_OS_BRIDGE
+  return llvm::Triple::BridgeOS;
+#else
+#error "LLDB being compiled for an unrecognized Darwin OS"
+#endif
+#endif // __APPLE__
+}

lldb/source/Plugins/Platform/MacOSX/PlatformMacOSX.cpp

ConstString PlatformMacOSX::GetSDKDirectory(lldb_private::Target &target) {
 
   return {};
 }
 
 std::vector<ArchSpec> PlatformMacOSX::GetSupportedArchitectures() {
   std::vector<ArchSpec> result;
 #if defined(__arm__) || defined(__arm64__) || defined(__aarch64__)
   // macOS for ARM64 support both native and translated x86_64 processes
-  ARMGetSupportedArchitectures(result, llvm::Triple::MacOSX);
 
+  // When cmdline lldb is run on iOS, watchOS, etc, it is still
+  // using "PlatformMacOSX".
+  llvm::Triple::OSType host_os = GetHostOSType();
+  ARMGetSupportedArchitectures(result, host_os);
+
+  if (host_os == llvm::Triple::MacOSX) {
     // We can't use x86GetSupportedArchitectures() because it uses
     // the system architecture for some of its return values and also
     // has a 32bits variant.
     result.push_back(ArchSpec("x86_64-apple-macosx"));
     result.push_back(ArchSpec("x86_64-apple-ios-macabi"));
     result.push_back(ArchSpec("arm64-apple-ios-macabi"));
     result.push_back(ArchSpec("arm64e-apple-ios-macabi"));
+  }
 #else
   x86GetSupportedArchitectures(result);
   result.push_back(ArchSpec("x86_64-apple-ios-macabi"));
 #endif
   return result;
 }
 
 lldb_private::Status PlatformMacOSX::GetSharedModule(