algorithm.cpp failed with clang-cl on Windows for "declaration does not declare anything"

[yuxianch]

With the latest version of clang-cl, algorithm.cpp get failed with clang-cl on Windows for "declaration does not declare anything".
Related code:

range/test/algorithm.cpp

Lines 32 to 35 in 72e2a44

	#ifdef _MSC_VER
	template ::boost::counting_iterator<int>;
	#pragma warning(pop)
	#endif

A small reproducer(test.cpp):

namespace boost {
  template <class T>
  class counting_iterator
  {};
}
template ::boost::counting_iterator<int>;

Error message:

ksh-3.2$ clang-cl -c test.cpp
test.cpp(6,10): error: declaration does not declare anything
template ::boost::counting_iterator<int>;
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.

The code is considered as not accepted(llvm/llvm-project@1cbdf93).