[ScanDependency][canImport] Improve canImport handling in explicit build

Teach dependency scanner to report all the module canImport check result
to swift-frontend, so swift-frontend doesn't need to parse swiftmodule
or parse TBD file to determine the versions. This ensures dependency
scanner and swift-frontend will have the same resolution for all
canImport checks.

This also fixes two related issues:
* Previously, in order to get consistant results between scanner and
  frontend, scanner will request building the module in canImport check
  even it is not imported later. This slightly alters the definition of
  the canImport to only succeed when the module can be found AND be
  built. This also can affect the auto-link in such cases.
* For caching build, the location of the clang module is abstracted away
  so swift-frontend cannot locate the TBD file to resolve
  underlyingVersion.

rdar://128067152

lib/DependencyScan/ModuleDependencyScanner.cpp

@@ -31,6 +31,7 @@
 #include "llvm/CAS/CachingOnDiskFileSystem.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/Threading.h"
+#include "llvm/Support/VersionTuple.h"
 #include "llvm/Support/VirtualFileSystem.h"
 #include <algorithm>
 
@@ -464,15 +465,26 @@ ModuleDependencyScanner::getMainModuleDependencyInfo(ModuleDecl *mainModule) {
                                         &ScanASTContext.SourceMgr);
     }
 
-    // Add all the successful canImport checks from the ASTContext as part of
-    // the dependency since only mainModule can have `canImport` check. This
-    // needs to happen after visiting all the top-level decls from all
+    // Pass all the successful canImport checks from the ASTContext as part of
+    // build command to main module to ensure frontend gets the same result.
+    // This needs to happen after visiting all the top-level decls from all
     // SourceFiles.
-    for (auto &Module :
-         mainModule->getASTContext().getSuccessfulCanImportCheckNames())
-      mainDependencies.addModuleImport(Module.first(),
-                                       &alreadyAddedModules);
-  }
+    auto buildArgs = mainDependencies.getCommandline();
+    mainModule->getASTContext().forEachCanImportVersionCheck(
+        [&](StringRef moduleName, const llvm::VersionTuple &Version,
+            const llvm::VersionTuple &UnderlyingVersion) {
+          if (Version.empty() && UnderlyingVersion.empty()) {
+            buildArgs.push_back("-module-can-import");
+            buildArgs.push_back(moduleName.str());
+          } else {
+            buildArgs.push_back("-module-can-import-version");
+            buildArgs.push_back(moduleName.str());
+            buildArgs.push_back(Version.getAsString());
+            buildArgs.push_back(UnderlyingVersion.getAsString());
+          }
+        });
+    mainDependencies.updateCommandLine(buildArgs);
+  }    
 
   return mainDependencies;
 }