Allow coverage with clang.

# clean build of your module after toggling it.

ifeq ($(NATIVE_COVERAGE),true)

    ifeq ($(my_native_coverage),true)

        # We can't currently generate coverage for clang binaries for two

        # reasons:

        my_cflags += --coverage -O0

        ifeq ($(my_clang),true)

            # b/17574078

            # We currently don't have a prebuilt libclang_rt.profile-<ARCH>.a,

            # which clang is hardcoded to link if --coverage is passed in the

            # link stage.  For now we manually link libprofile_rt (which is the

            # name it is built as from external/compiler-rt).

            #

        # 1) b/17574078 We currently don't have a prebuilt

        #    libclang_rt.profile-<ARCH>.a, which clang is hardcoded to link if

        #    --coverage is passed in the link stage. For now we manually link

        #    libprofile_rt (which is the name it is built as from

        #    external/compiler-rt).

            # Note that clang coverage doesn't play nicely with acov out of the

            # box. Clang apparently generates .gcno files that aren't compatible

            # with gcov-4.8.  This can be solved by installing gcc-4.6 and

            # invoking lcov with `--gcov-tool /usr/bin/gcov-4.6`.

            #

        # 2) b/17583330 Clang doesn't generate .gcno files when using

        #    -no-integrated-as. Since most of the assembly in our tree is

        #    incompatible with clang's assembler, we can't turn off this flag.

        ifneq ($(my_clang),true)

            my_cflags += --coverage -O0

            # http://stackoverflow.com/questions/17758126/clang-code-coverage-invalid-output

            my_static_libraries += libprofile_rt

        else

            my_ldflags += --coverage

        endif

    endif