The previous strategy of force-inlining methods that are dependent
on the library version is not effective with MSVC in debug mode,
when linking the static library. The compiler does not inline
methods despite the markup, and during linking the static library
with the user's module the linker may or may not pick up user's
definitions of these methods.
When building the library, do not define path methods that depend
on the library version. Instead, explicitly call v4 internal methods
throughout the implementation. This way the compiled library does not
contain v4 versions of these methods, and therefore does not conflict
with user's definitions of these methods.
Fixes https://github.com/boostorg/filesystem/issues/279.
