Make abseil a public dependency of libprotobuf (#10460)

descriptor.h includes abseil's mutex.h directly, thus abseil is not a
private dependency any more but must be included by every user of
libprotobuf.

Co-authored-by: Harald Fernengel <547273+haraldF@users.noreply.github.com>
diff --git a/cmake/libprotoc.cmake b/cmake/libprotoc.cmake
index b3a907f..3be0df3 100644
--- a/cmake/libprotoc.cmake
+++ b/cmake/libprotoc.cmake
@@ -16,8 +16,7 @@
     LINK_DEPENDS ${protobuf_SOURCE_DIR}/src/libprotoc.map)
 endif()
 target_link_libraries(libprotoc PRIVATE libprotobuf)
-target_link_libraries(libprotoc PRIVATE ${protobuf_ABSL_USED_TARGETS})
-target_include_directories(libprotoc PRIVATE ${ABSL_ROOT_DIR})
+target_link_libraries(libprotoc PUBLIC ${protobuf_ABSL_USED_TARGETS})
 if(protobuf_BUILD_SHARED_LIBS)
   target_compile_definitions(libprotoc
     PUBLIC  PROTOBUF_USE_DLLS