Blink's "assembly tests" are tests written in pure assembly that we run both in Blink and on bare metal.
Compilers only utilize a subset of what the instruction set architecture
is capable of doing. For example, CMPXCHG is able to set the overflow
flag under certain conditions, but that would never matter to any C code
that's compiled by GCC. Another example is the clearing of the upper
half of registers on 32-bit operations. We need to ensure that Blink
will always do that when appropriate, just as the host hardware would.
However C code may be unlikely to catch when this happening.
In host environments that aren't AMD64 Linux, bare metal testing will be
stubbed out using $(VM). Therefore this test suite will still pass,
but it'll only be 100% useful when it's run on an x86_64-linux system.