sigchain: dlsym from libc.so instead of RTLD_NEXT.

RTLD_NEXT doesn't play well with linker namespaces currently, so switch
to directly referencing libc.so.

Bug: http://b/135284876
Test: treehugger
Test: m test-art-host
Test: adb shell /data/nativetest/art/arm/art_sigchain_tests/sigchain_test
Test: adb shell /data/nativetest64/art/arm64/art_sigchain_tests/sigchain_test
Change-Id: I980bf63e5e3bb0a1638a4806c7ad76f41d5db44e
1 file changed