Arm64 macOS doesn't support long double

[suborb]

Which results in a bunch of warnings when using 64 bit integers in sccz80:

rshift.c:525:31: warning: On this host, 64 bit constants may not be correct

This is an apple thing, since floats larger than 64 bits are available on Linux/arm64

We use a long double to hold constant values, falling back to a double means that we're missing 10/11 bits of mantissa precision for a lossless conversion to a uint64_t/int64_t

Given how little 64 bit values are used, it's not massively important, but I should fix it.

[suborb]

Also related, to recent armhf failures on snap craft:

zcc +test -vn  -I../../framework -DNO_LOG_RUNNING -DNO_LOG_PASSED ../../framework/test.c mult.c -o test_mult.bin  -m
mult.c:37:50: warning: On this host, 64 bit constants may not be correct
 [-Wlimited-range]
mult.c:53:33: warning: On this host, 64 bit constants may not be correct
 [-Wlimited-range]
mult.c:54:33: warning: On this host, 64 bit constants may not be correct
 [-Wlimited-range]
mult.c:56:29: warning: On this host, 64 bit constants may not be correct
 [-Wlimited-range]
mult.c:57:29: warning: On this host, 64 bit constants may not be correct
 [-Wlimited-range]
 06:39:09  Starting test 
Starting suite Multiplication Tests (7 tests)
Running test test_mult_unsigned_longlong.....failed mult.c:53 (3 * 0x2AAAAAAAAAAAAAAB)
7 run, 6 passed, 1 failed

Ticks: 579522
 06:39:09  Test failure