Create RAII lock guard for global initialization lock. am: f0dede204c am: 37f4e675ec am: e0db87d67e am: 42308500ae

Original change: https://android-review.googlesource.com/c/platform/external/libcxxabi/+/1727431

Change-Id: I5c14642b7b9490dcc7bc1a4c0539c3ad2c0adbca