cmake: define interface include directories

Summary:
Define interface include directories for the folly target.

This lets downstream dependencies of folly list Folly::folly in
target_link_libraries() and have the correct include directories be
added automatically.

Reviewed By: yfeldblum

Differential Revision: D7162335

fbshipit-source-id: 2a6aad57142e038450fd35a94446f5b865029155

CMakeLists.txt

@@ -267,12 +267,20 @@ add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/folly_dep.cpp
   COMMAND ${CMAKE_COMMAND} -E touch ${CMAKE_CURRENT_BINARY_DIR}/folly_dep.cpp
   DEPENDS folly_base folly_fingerprint
 )
-add_library(folly ${CMAKE_CURRENT_BINARY_DIR}/folly_dep.cpp $<TARGET_OBJECTS:folly_base>)
+add_library(folly
+  ${CMAKE_CURRENT_BINARY_DIR}/folly_dep.cpp
+  $<TARGET_OBJECTS:folly_base>
+)
 apply_folly_compile_options_to_target(folly)
 source_group("" FILES ${CMAKE_CURRENT_BINARY_DIR}/folly_dep.cpp)
 
 target_link_libraries(folly PUBLIC ${FOLLY_LINK_LIBRARIES})
-target_include_directories(folly PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}>)
+target_include_directories(folly
+  INTERFACE
+    ${FOLLY_INCLUDE_DIRECTORIES}
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}>
+    $<INSTALL_INTERFACE:include>
+)
 
 install(TARGETS folly
   EXPORT folly