This patch fixes a bunch of bugs in the fallback implementation of is_convertible, which is used by GCC. Removing the "__is_convertible" specializations for array/function types we fallback on the SFINAE test, which is more correct. See https://llvm.org/bugs/show_bug.cgi?id=27538 git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@268359 91177308-0d34-0410-b5e6-96231b3b80d8