Include libprofile-extras to all coverage variants

Bug: http://b/128524141

Include libprofile-extras (defined in system/extras/toolchain-extras) to
all modules that need a coverage variant.  Also add
'-uinit_profile_extras' when linking with coverage.  This causes the
setup code in libprofile-extras to be linked into binaries/libraries
with coverage enabled.

We add the static library to the non-coverage variants as well but is a
no-op for them (since the '-u...' flag is not added for them).

Adding this dependency creates several circular dependencies since
coverage variants were being created for other module types that never
had any compilation or linking done during the build.  This change stops
creating coverage variants for toolchain_library, cc_prebuilt_library_*,
cc_library_headers module types (by adding a function to the linker
interface to specify whether native coverage is enabled).

Test: m NATIVE_COVERAGE=true COVERAGE_PATHS=*
Test: blueline_coverage target in internal branch (using forrest)
Change-Id: I5db876eb953639a55ba007248dd24e497f987730