cmCxxModuleMapper: give transitive usages to Clang as well

In the future, Clang plans to require transitive module usage to be
specified on the command line. This is in order to keep BMI files more
reproducible. Handily, MSVC has already required this, so the logic can
be reused for Clang easily.

See: llvm/llvm-project@e22fa1d
See: llvm/llvm-project#62707
See: https://discourse.llvm.org/t/c-20-modules-should-the-bmis-contain-paths-to-their-dependent-bmis/70422

Author: mathstuf

Source/cmCxxModuleMapper.cxx

@@ -128,7 +128,8 @@ std::vector<TransitiveUsage> GetTransitiveUsages(
 }
 
 std::string CxxModuleMapContentClang(CxxModuleLocations const& loc,
-                                     cmScanDepInfo const& obj)
+                                     cmScanDepInfo const& obj,
+                                     CxxModuleUsage const& usages)
 {
   std::stringstream mm;
 
@@ -151,12 +152,11 @@ std::string CxxModuleMapContentClang(CxxModuleLocations const& loc,
       break;
     }
   }
-  for (auto const& r : obj.Requires) {
-    auto bmi_loc = loc.BmiGeneratorPathForModule(r.LogicalName);
-    if (bmi_loc.IsKnown()) {
-      mm << "-fmodule-file=" << r.LogicalName << "=" << bmi_loc.Location()
-         << '\n';
-    }
+
+  auto all_usages = GetTransitiveUsages(loc, obj.Requires, usages);
+  for (auto const& usage : all_usages) {
+    mm << "-fmodule-file=" << usage.LogicalName << '=' << usage.Location
+       << '\n';
   }
 
   return mm.str();
@@ -420,7 +420,7 @@ std::string CxxModuleMapContent(CxxModuleMapFormat format,
 {
   switch (format) {
     case CxxModuleMapFormat::Clang:
-      return CxxModuleMapContentClang(loc, obj);
+      return CxxModuleMapContentClang(loc, obj, usages);
     case CxxModuleMapFormat::Gcc:
       return CxxModuleMapContentGcc(loc, obj);
     case CxxModuleMapFormat::Msvc: