fix anttweakbar includes

Former-commit-id: 1eafacccdbb1067038786a4b94020edd2f0b6be8

shared/cmake/libigl.cmake

@@ -185,6 +185,7 @@ if(LIBIGL_WITH_ANTTWEAKBAR)
   endif()
   compile_igl_module("anttweakbar")
   target_link_libraries(igl_anttweakbar ${IGL_SCOPE} AntTweakBar)
+  target_include_directories(igl_anttweakbar ${IGL_SCOPE} "${ANTTWEAKBAR_DIR}/include")
 endif()
 
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