Ninja: properly handle exports from Swift exes

This adds logic to properly handle Swift executables.  Only executables
marked as exporting symbols will now generate module interfaces for the
executable.

Modules/CMakeSwiftInformation.cmake

@@ -17,6 +17,8 @@ if(CMAKE_Swift_COMPILER_ID)
   include(Platform/${CMAKE_EFFECTIVE_SYSTEM_NAME}-${CMAKE_Swift_COMPILER_ID}-Swift OPTIONAL)
 endif()
 
+set(CMAKE_EXE_EXPORTS_Swift_FLAG "-emit-module -emit-module-path <SWIFT_MODULE> ${CMAKE_Swift_IMPLIB_LINKER_FLAGS}")
+
 set(CMAKE_INCLUDE_FLAG_Swift "-I ")
 if(CMAKE_SYSTEM_NAME STREQUAL Darwin)
   set(CMAKE_SHARED_LIBRARY_SONAME_Swift_FLAG "-Xlinker -install_name -Xlinker ")
@@ -81,7 +83,7 @@ if(NOT CMAKE_Swift_CREATE_SHARED_MODULE)
 endif()
 
 if(NOT CMAKE_Swift_LINK_EXECUTABLE)
-  set(CMAKE_Swift_LINK_EXECUTABLE "<CMAKE_Swift_COMPILER> -output-file-map <SWIFT_OUTPUT_FILE_MAP> -incremental -j ${CMAKE_Swift_NUM_THREADS} -emit-executable -o <TARGET> -emit-module -emit-module-path <SWIFT_MODULE> -emit-dependencies <DEFINES> <FLAGS> <INCLUDES> <SWIFT_SOURCES> <LINK_FLAGS> ${CMAKE_Swift_IMPLIB_LINKER_FLAGS} <LINK_LIBRARIES>")
+  set(CMAKE_Swift_LINK_EXECUTABLE "<CMAKE_Swift_COMPILER> -output-file-map <SWIFT_OUTPUT_FILE_MAP> -incremental -j ${CMAKE_Swift_NUM_THREADS} -emit-executable -o <TARGET> -emit-dependencies <DEFINES> <FLAGS> <INCLUDES> <SWIFT_SOURCES> <LINK_FLAGS> <LINK_LIBRARIES>")
 endif()
 
 if(NOT CMAKE_Swift_CREATE_STATIC_LIBRARY)

Source/cmNinjaNormalTargetGenerator.cxx

@@ -550,16 +550,23 @@ std::vector<std::string> cmNinjaNormalTargetGenerator::ComputeLinkCmd(
         linkCmds.push_back(cmakeCommand + " -E touch $TARGET_FILE");
       }
 #endif
-      return linkCmds;
-    }
+    } break;
     case cmStateEnums::SHARED_LIBRARY:
     case cmStateEnums::MODULE_LIBRARY:
+      break;
     case cmStateEnums::EXECUTABLE:
+      if (this->TargetLinkLanguage(config) == "Swift") {
+        if (this->GeneratorTarget->IsExecutableWithExports()) {
+          const std::string flags =
+            this->Makefile->GetSafeDefinition("CMAKE_EXE_EXPORTS_Swift_FLAG");
+          cmExpandList(flags, linkCmds);
+        }
+      }
       break;
     default:
       assert(false && "Unexpected target type");
   }
-  return std::vector<std::string>();
+  return linkCmds;
 }
 
 void cmNinjaNormalTargetGenerator::WriteDeviceLinkStatement(