Regression in C++ standard compatibility

[valgur]

I was updating the plf_list recipe for Conan Center (https://github.com/conan-io/conan-center-index/pull/21933) and noticed that after a version bump from v2.57 to v2.70 the library no longer only compiles without issues with the C++17 standard and compatible compiler versions. Older compiler versions (GCC < 7 and Clang < 5) fail with

In file included from plf_list/all/test_package/test_package.cpp:1:0:
plf_list.h: In member function ‘plf::list<element_type, allocator_type>::iterator plf::list<element_type, allocator_type>::unordered_find_single(const element_type&) const’:
plf_list.h:3497:45: error: missing template arguments before ‘(’ token
   return unordered_find_single(plf::equal_to(element_to_match));
                                             ^
plf_list.h: In member function ‘plf::list<plf::list<element_type, allocator_type>::list_iterator<false> > plf::list<element_type, allocator_type>::unordered_find_multiple(const element_type&, plf::list<element_type, allocator_type>::size_type) const’:
plf_list.h:3584:47: error: missing template arguments before ‘(’ token
   return unordered_find_multiple(plf::equal_to(element_to_match), number_to_find);
                                               ^
plf_list.h: In member function ‘plf::list<plf::list<element_type, allocator_type>::list_iterator<false> > plf::list<element_type, allocator_type>::unordered_find_all(const element_type&) const’:
plf_list.h:3651:42: error: missing template arguments before ‘(’ token
   return unordered_find_all(plf::equal_to(element_to_match));

I thought you might want to know as the stated expected compatibility is for C++98.