Don't specify visibility attributes for static libraries

[FooIbar]

This was introduced in #1751 and will cause those symbols get exported when static libarchive is linked to a shared library.

[kientzle]

CC: @evelikov

[evelikov]

At a glance a few preexisting issues have contributed to this:

• internal specifics __LA_DECL and by extension LIBARCHIVE_STATIC and __LIBARCHIVE_BUILD have made their way into the public headers

In one of my projects, I a) defined FOO_API symbol internally for non-win32 gnuc builds (stub elsewhere) and b) annotated the definition (aka c file). The windows (msvc or mingw) builds are using a .spec file listing the exported symbols.

This would be my top recommendation.

• the existing if/else chain is borderline incomprehensive

If the above suggestion doesn't fly, something like the following should be much better IMHO.

#if defined foo_static
#define foo /* dummy */
#if defined _WIN32 // no need for __WIN32__ or cygwin
#elif defined libarchive_building
#define foo __declspec(dllexport) // no need for gnu variant, gcc 4.0 (and maybe earlier) supports the msvc syntax
#else
#define foo __declspec(dllimport) // ditto no need for gnuc/gcc check
#endif
#elif defined __GNUC__ && __GNUC__ >= 4 // this is the explicit recommendation by the GCC docs, over the manual in-configure checks 
#define foo __attribute...
#else
#define foo /* dummy */
#endif

Hope that helps.

[evelikov]

@kientzle would love to hear you opinion if the former option is something the team is happy with.