Make auto scheduler libs available in HalideHelpers package (#7285)

* Make auto scheduler libs available in HalideHelpers package

find_package(HalideHelpers) allows us to use add_halide_library().
But auto scheduler libs are not available unless they are in
Halide-Interfaces.cmake.
Note:
Those libraries are not actually linked to the target application,
but need to be available for add_custom_command call.

packaging/CMakeLists.txt

@@ -33,7 +33,7 @@ install(TARGETS Halide Halide_Generator Halide_LanguageOptions
 
 if (TARGET Halide_Adams2019)
     install(TARGETS Halide_Adams2019 Halide_Li2018 Halide_Mullapudi2016
-            EXPORT Halide_Targets
+            EXPORT Halide_Interfaces
             LIBRARY DESTINATION ${Halide_INSTALL_PLUGINDIR} COMPONENT Halide_Runtime
             NAMELINK_COMPONENT Halide_Development)
 endif ()