8229258: Backport patch from JDK 14 to allow building with Clang 13

This patch backports changes from JDK14 commit ae5615c6142a4dc0d9033462f4880d7b3c127e26. It does not rename the class to markWord as the original patch does, but instead converts markOop to a markWord equivalent in-place. This patch allows the JDK to be built with Clang 13, as it avoids undefined behavior. See here: https://bugs.openjdk.java.net/browse/JDK-8229258

Bug: 197273045
Test: builds
Change-Id: Ie7501cf66eb03e4bc5f30ea4fb0af9fd8fe16d38
103 files changed