add an explanatory comment.

llvm-svn: 33565

llvm/test/C++Frontend/2003-11-02-WeakLinkage.cpp.tr

 // RUN: %llvmgcc -xc++ -S -o - %s | not grep weak
 // XFAIL: llvmgcc4
+// The template should compile to linkonce linkage, not weak linkage.
 
 template<class T>
 void thefunc();