Clang compilation targets may support `__declspec` attributes. Because of that it has a `__has_declspec_attribute` [check](https://clang.llvm.org/docs/LanguageExtensions.html#has-declspec-attribute).
Currently libpsl just assumes that `__declspec` is Windows only. This adds a compatibility macro and checks whether `dllimport` and `dllexport` are available.
Introduce a macro, PSL_PUBLIC, which is defined as nothing by default,
which can be used by the compiler to instruct the linker to export the
public symbols, such as __declspec (dllexport) on Visual Studio.
When writing a wrapper around LibPSL in a different language it is
important that libpsl provide functions to free any memory that it
allocates. Without this, it is impossible to correctly free the memory
allocated by psl_str_to_utf8lower() function since in other languages
one may not have access to the same free() call from libc.
Also add a new ./configure function to set a distribution wide
PSL file used by psl_latest(): --with-psl-distfile
If possible that filename should point to a DAFSA PSL file that
becomes updated regularly.
Tim Rühsen
Don
Chun-wei Fan
Claudio Saavedra
Darshit Shah
Daniel Kahn Gillmor