Support building on macosx-arm64

[brendo-m]

Supporting cross compiling from an M1 mac.

I had to disable the sqlite_from_macosx-arm64_to_linux-amd64-gnu.2.27 test, it fails with error

ld.lld: error: undefined symbol: fcntl64
>>> referenced by sqlite3.c
>>>               /Users/brendan/.cache/nim/main_d/sqlite3.c.o:(aSyscall)
Error: execution of an external program failed: '/Users/brendan/workspace/nim/brendo-m/nimxc/_tests/toolchains/zig-macos-aarch64-0.9.0/zigcc   -o /Users/brendan/workspace/nim/brendo-m/nimxc/_tests/tests/sqlite_from_macosx-arm64_to_linux-amd64-gnu.2.27/main  /Users/brendan/.cache/nim/main_d/sqlite3.c.o /Users/brendan/.cache/nim/main_d/@m..@s..@s..@s..@s..@s..@s..@s..@s..@sopt@shomebrew@sCellar@snim@s1.6.10@snim@slib@sstd@sprivate@sdigitsutils.nim.c.o /Users/brendan/.cache/nim/main_d/@m..@s..@s..@s..@s..@s..@s..@s..@s..@sopt@shomebrew@sCellar@snim@s1.6.10@snim@slib@ssystem@sassertions.nim.c.o /Users/brendan/.cache/nim/main_d/@m..@s..@s..@s..@s..@s..@s..@s..@s..@sopt@shomebrew@sCellar@snim@s1.6.10@snim@slib@ssystem@sdollars.nim.c.o /Users/brendan/.cache/nim/main_d/@m..@s..@s..@s..@s..@s..@s..@s..@s..@sopt@shomebrew@sCellar@snim@s1.6.10@snim@slib@spure@scollections@ssharedlist.nim.c.o /Users/brendan/.cache/nim/main_d/@m..@s..@s..@s..@s..@s..@s..@s..@s..@sopt@shomebrew@sCellar@snim@s1.6.10@snim@slib@ssystem@sio.nim.c.o /Users/brendan/.cache/nim/main_d/@m..@s..@s..@s..@s..@s..@s..@s..@s..@sopt@shomebrew@sCellar@snim@s1.6.10@snim@slib@ssystem.nim.c.o /Users/brendan/.cache/nim/main_d/@m..@s..@s..@s..@s..@s..@s..@s..@s..@sopt@shomebrew@sCellar@snim@s1.6.10@snim@slib@spure@sdb_common.nim.c.o /Users/brendan/.cache/nim/main_d/@m..@s..@s..@s..@s..@s..@s..@s..@s..@sopt@shomebrew@sCellar@snim@s1.6.10@snim@slib@simpure@sdb_sqlite.nim.c.o /Users/brendan/.cache/nim/main_d/@mmain.nim.c.o  -pthread -lpthread  -target x86_64-linux-gnu.2.27 -fno-sanitize=undefined  -ldl'
# rc = 1
/Users/brendan/workspace/nim/brendo-m/nimxc/tests/test_everything.nim(69, 17): Check failed: rc == 0
rc was 1
[FAILED] sqlite_from_macosx-arm64_to_linux-amd64-gnu.2.27

This is an issue in ziglang itself and might be fixed in the next few releases. ziglang/zig#9485

[iffy]

Looks good to me! I'll merge when the tests pass.