Usage of uninitialized memory is a top memory safety issue in C++ codebases.
Help mitigate this somewhat by default initialize stack allocations to a
pattern (0xAA repeating).
Clang has received optimizations to sink these into control flow paths that
access such values to minimize the overhead of these added initializations.
If there's a measurable slowdown, we can add
-ftrivial-auto-var-init-max-size=<N> for some value N bytes if we have any
large stack allocations, or add attribute uninitialized to any variable
declarations.
Unsupported until GCC 12.1 / Clang 8.
Increases file size of libc.a from a full build by +8.79Ki (+0.2%).
