Implement for vanilla SwiftPM builds

Author: matthewseaman

Sources/Build/BuildDescription/ClangModuleBuildDescription.swift

@@ -455,6 +455,12 @@ public final class ClangModuleBuildDescription {
             break
         }
 
+        if bundlePath != nil {
+            compilationConditions += ["-DSWIFT_MODULE_RESOURCE_BUNDLE_AVAILABLE=1"]
+        } else {
+            compilationConditions += ["-DSWIFT_MODULE_RESOURCE_BUNDLE_UNAVAILABLE=1"]
+        }
+
         return compilationConditions
     }