reduces SRAM usage. Refer to `Library at ROM`_ for further details. Default
is 0.
+- ``USE_SPINLOCK_CAS``: Setting this build flag to 1 selects the spinlock
+ implementation variant using the ARMv8.1-LSE compare-and-swap instruction.
+ Notice this option is experimental and only available to AArch64 builds.
+
- ``V``: Verbose build. If assigned anything other than 0, the build commands
are printed. Default is 0.