SILOptimizer: rename cdecl to ctor (NFC)

`cdecl` is a keyword in the non-conforming C++ dialect used on Windows
which expands to `__cdecl`.  Simply rename the variable to avoid the
replacement.  Although it is possible to `#undef cdecl`, renaming makes
it less confusing for non-Windows developers.

Author: compnerd

lib/SILOptimizer/Mandatory/OSLogOptimization.cpp

@@ -792,10 +792,10 @@ bool isAutoGeneratedInitOfOSLogMessage(SILFunction &fun) {
   Decl *decl = declContext->getAsDecl();
   if (!decl)
     return false;
-  ConstructorDecl *cdecl = dyn_cast<ConstructorDecl>(decl);
-  if (!cdecl)
+  ConstructorDecl *ctor = dyn_cast<ConstructorDecl>(decl);
+  if (!ctor)
     return false;
-  DeclContext *parentContext = cdecl->getParent();
+  DeclContext *parentContext = ctor->getParent();
   if (!parentContext)
     return false;
   NominalTypeDecl *typeDecl = parentContext->getSelfNominalTypeDecl();