[Issue 19499] __c_long_double brake template specialization

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19499

--- Comment #4 from Walter Bright <bugzilla at digitalmars.com> ---
A self-contained test case:

  enum __c_long_double : double;
  enum A(T : double) = true;
  enum A(T : __c_long_double) = false;
  pragma(msg, A!double);

test.d(6): Error: template test.A matches more than one template declaration:
test.d(4):     A(T : double)
and
test.d(5):     A(T : __c_long_double)
test.d(6):        while evaluating pragma(msg, A!double)

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