Solve -ftrivial-auto-var-init performance regression with QEMU_UNINITIALIZED

Merge Request Required Information

Summary of Changes

The -ftrivial-auto-var-init compiler flag zeroes stack variables to reduce the risk of uninitialized variable accesses. The introduction of this compiler flag caused a performance regression because some hot code paths in QEMU have large stack buffers.

Mark these buffers with the new QEMU_UNINITIALIZED macro, which disabled -ftrivial-auto-var-init for a single variable. This solves the performance regression while keeping -ftrivial-auto-var-init protection for most variables.

Approved Development Ticket(s)

Resolves: RHEL-95479
Jira: https://issues.redhat.com/browse/RHEL-95479
Signed-off-by: Stefan Hajnoczi stefanha@redhat.com
Brew: https://brewweb.engineering.redhat.com/brew/taskinfo?taskID=68027445