fix: do not add include/roaring to the includes

Only add `include/`, so includes must be done as `<roaring/xxx.h>`. Also, fix
an issue where `CMAKE_INSTALL_INCDIR` was referenced, the correct variable is
`CMAKE_INSTALL_INCLUDEDIR`:

https://cmake.org/cmake/help/latest/command/install.html

CMakeLists.txt

@@ -74,12 +74,12 @@ install(FILES "${CMAKE_CURRENT_BINARY_DIR}/roaring.pc" DESTINATION ${CMAKE_INSTA
 
 add_library(roaring-headers INTERFACE)
 target_include_directories(roaring-headers INTERFACE
-  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include/roaring>
-  $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCDIR}>)
+  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
+  $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>)
 add_library(roaring-headers-cpp INTERFACE)
 target_include_directories(roaring-headers-cpp INTERFACE
   $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/cpp>
-   $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCDIR}>)
+   $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>)
 
 ####
 ### Some users want the C++ header files to be installed as well.
@@ -93,7 +93,7 @@ install(TARGETS roaring-headers roaring-headers-cpp
    ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
-   INCLUDES DESTINATION ${CMAKE_INSTALL_INCDIR})
+   INCLUDES DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
 include(CTest)
 
 ##################################

src/CMakeLists.txt

@@ -59,12 +59,6 @@ if(ROARING_DISABLE_NEON)
   target_compile_definitions(roaring PUBLIC DISABLENEON=1)
 endif(ROARING_DISABLE_NEON)
 
-
-target_include_directories(roaring
-  PUBLIC
-   $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>
-   $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
-)
 target_link_libraries(roaring PUBLIC roaring-headers)
 target_link_libraries(roaring PUBLIC roaring-headers-cpp)
 #
@@ -75,7 +69,7 @@ install(TARGETS roaring
    ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
-   INCLUDES DESTINATION ${CMAKE_INSTALL_INCDIR}
+   INCLUDES DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
 )
 install(EXPORT roaring-config
    FILE roaring-config.cmake