[clang][OpenMP][CodeGen] Use an else if instead of checking twice (#168776)

These two classes are mutually exclusive so avoid doing the two checks
when the first succeeded.

Author: rofirrim

clang/lib/CodeGen/CGStmtOpenMP.cpp

@@ -1950,9 +1950,9 @@ class OMPTransformDirectiveScopeRAII {
       Scope = new OMPLoopScope(CGF, *Dir);
       CGSI = new CodeGenFunction::CGCapturedStmtInfo(CR_OpenMP);
       CapInfoRAII = new CodeGenFunction::CGCapturedStmtRAII(CGF, CGSI);
-    }
-    if (const auto *Dir =
-            dyn_cast<OMPCanonicalLoopSequenceTransformationDirective>(S)) {
+    } else if (const auto *Dir =
+                   dyn_cast<OMPCanonicalLoopSequenceTransformationDirective>(
+                       S)) {
       // For simplicity we reuse the loop scope similarly to what we do with
       // OMPCanonicalLoopNestTransformationDirective do by being a subclass
       // of OMPLoopBasedDirective.