libstdc++: Inline all basic_string::compare overloads [PR59048]

libstdc++: Inline all basic_string::compare overloads [PR59048]

Defining the compare member functions inline allows calls to
traits_type::length and std::min to be inlined, taking advantage of
constant expression arguments. When not inline, the compiler prefers to
use the explicit instantiation definitions in libstdc++.so and can't
take advantage of constant arguments.

libstdc++-v3/ChangeLog:

	PR libstdc++/59048
	* include/bits/basic_string.h (compare): Define inline.
	* include/bits/basic_string.tcc (compare): Remove out-of-line
	definitions.
	* include/bits/cow_string.h (compare): Define inline.
	* testsuite/21_strings/basic_string/operations/compare/char/3.cc:
	New test.