vdso should be available in all namespaces

vdso should be available in all namespaces when present. This
bug went undetected because the way libc currently uses vdso (it
does all the lookups itself). This makes it available for the
programs that want to take advantage by dlopening it.

Bug: http://b/73105445
Bug: http://b/79561555
Test: adb shell /data/nativetest/arm/bionic-unit-tests/bionic-unit-tests --gtest_filter=dl.exec_with_ld_config_file
Test: adb shell /data/nativetest/bionic-unit-tests/bionic-unit-tests --gtest_filter=dl*
Change-Id: I8eae0c9848f256190d1c9ec85d10dc6ce383a8bc