[libc++] Improve CMake include directory search.

[Mordante]

Summary

This patch has been tested in D70631, but it should be reviewed
separately.

[ldionne]

libcxx/src/CMakeLists.txt

200

What are these useful for?

[Mordante]

libcxx/src/CMakeLists.txt

200

Basically it's based on the comment https://reviews.llvm.org/D70631#inline-1071881. In that original version I used the blunt tool of include_directories(${CMAKE_CURRENT_SOURCE_DIR}). Without this the ryu related headers can't be found.

[ldionne]

libcxx/src/CMakeLists.txt

200

Thanks!

libcxx/src/CMakeLists.txt

 endfunction()
 
 split_list(LIBCXX_COMPILE_FLAGS)
 split_list(LIBCXX_LINK_FLAGS)
 
 # Build the shared library.
 if (LIBCXX_ENABLE_SHARED)
   add_library(cxx_shared SHARED ${exclude_from_all} ${LIBCXX_SOURCES} ${LIBCXX_HEADERS})
+  target_include_directories(cxx_shared PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
   target_link_libraries(cxx_shared PUBLIC cxx-headers
                                    PRIVATE ${LIBCXX_LIBRARIES})
   set_target_properties(cxx_shared
     PROPERTIES
       COMPILE_FLAGS "${LIBCXX_COMPILE_FLAGS}"
       LINK_FLAGS    "${LIBCXX_LINK_FLAGS}"
       OUTPUT_NAME   "c++"
       VERSION       "${LIBCXX_ABI_VERSION}.0"
if (LIBCXX_ENABLE_SHARED)
   endif()
 endif()
 
 set(CMAKE_STATIC_LIBRARY_PREFIX "lib")
 
 # Build the static library.
 if (LIBCXX_ENABLE_STATIC)
   add_library(cxx_static STATIC ${exclude_from_all} ${LIBCXX_SOURCES} ${LIBCXX_HEADERS})
+  target_include_directories(cxx_static PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
   target_link_libraries(cxx_static PUBLIC cxx-headers
                                    PRIVATE ${LIBCXX_LIBRARIES})
   set_target_properties(cxx_static
     PROPERTIES
       COMPILE_FLAGS "${LIBCXX_COMPILE_FLAGS}"
       LINK_FLAGS    "${LIBCXX_LINK_FLAGS}"
       OUTPUT_NAME   "c++"
       POSITION_INDEPENDENT_CODE ON