Allow parenthesized expressions as the value of defines

For example, this now works:

#define A (1 + 2)

Note that we still don't support defines with argument lists, so this is
still illegal:

#define A(X) (X + 2)

Also in this change: The compiler test script allows command-line
arguments to disable testing on ARM and to disable testing the output
of the old OTCC compiler.

Disabling testing on ARM is handy for developing front-end code when no
device or emulator is available.

Disabling testing OTCC output is handy for some 64-bit Linux environments,
because the original OTCC needs some tweaking to be fully compatible, and
I don't have time to investigate this problem right now.