Zstd: cmake target libzstd_static does not export public include directory

[mateuszzz88]

This is a regression that happened in 1.3.5.
With zstd 1.3.4 I could use library as subproject in cmake, without global install

1. put the whole source in my project,
2. in CMake add subdirectory: add_subdirectory(zstd-1.3.4/build/cmake)
3. In CMake in my target add target_link_library(my_target PRIVATE libzstd_static)
4. Use library with #include

With 1.3.5 and 1.3.7 this fails with "zstd.h file not found".

[mateuszzz88]

ok, possibly this is not regression - I may have modified 1.3.4 locally.
Anyway,
target_include_directories(libzstd_static INTERFACE ${LIBRARY_DIR}) is needed in build/cmake/lib/CMakeLists.txt and similar for shared version.

[Cyan4973]

We accept PR on this topic

[hjmjohnson]

FYI: #1474, #1475 are precursors towards being able to support this use-case robustly.

[Cyan4973]

With both #1474 and #1475 merged, I guess this topic is covered now.