Extend GCC workaround to GCC < 8.4 for llvm::iterator_range ctor (#82643)

GCC SFINAE error with decltype was fixed in commit
ac5e28911abdfb8d9bf6bea980223e199bbcf28d which made it into GCC 8.4.
Therefore adjust GCC version test accordingly.

(cherry picked from commit 7f71fa90)