Disable native_coverage for libdl

Bug: http://b/116873221
Bug: http://b/124067925

If not,
https://android-review.googlesource.com/c/platform/build/soong/+/848621
breaks blueline_coverage-userdebug target in internal branches with the
following error:
    build/make/core/base_rules.mk:290: error: bionic/libdl:
    MODULE.TARGET.SHARED_LIBRARIES.libdl already defined by
    bionic/libdl.

Test: build blueline_coverage-userdebug in internal branch.

Change-Id: I8fff866ae2e17ce6daa4d8c75c72ceb17e2e73de