Without this, stack-use-after-scope can only be detected at runtime with ASan or code review, both of which are expensive.

Use LIFETIMEBOUND to turn this error into a compile warning.

See https://releases.llvm.org/12.0.0/tools/clang/docs/AttributeReference.html#lifetimebound

Example:

const CScript a{WITH_LOCK(::cs_main, return CScript{} << OP_0 << OP_1)};

Before: (no warning)
After:

warning: returning reference to local temporary object [-Wreturn-stack-address]
    const CScript a{WITH_LOCK(::cs_main, return CScript{} << OP_0 << OP_1)};
                                                ^~~~~~~~~
./sync.h:276:65: note: expanded from macro 'WITH_LOCK'
                                                                ^~~~

ninja all check