MacOS CI: Now running on ARM64 CPUs

[mratsim]

It seems like assembly for Apple Clang changed:

https://github.com/mratsim/constantine/actions/runs/8862799707/job/24336160802?pr=370

/Users/runner/work/constantine/constantine/constantine/nimcache/libcurves_headers/@m..@sconstantine@splatforms@sisa@scpudetect_x86.nim.c:80:8: error: invalid output constraint '=a' in asm
      :"=a"(result.eax), "=b"(result.ebx), "=c"(result.ecx), "=d"(result.edx)
       ^

constantine/constantine/platforms/isa/cpudetect_x86.nim

Lines 17 to 36 in 976c8bb

	proc cpuid(eax: uint32, ecx = 0'u32): CpuIdRegs =
	## Query the CPU
	##
	## CPUID is a very slow operation, 27-70 cycles, ~120 latency
	## - https://uops.info/table.html
	## - https://www.agner.org/optimize/instruction_tables.pdf
	##
	## and need to be cached if CPU capabilities are needed in a hot path
	when defined(vcc):
	# limited inline asm support in MSVC, so intrinsics, here we go:
	proc cpuidMSVC(cpuInfo: ptr uint32; functionID, subFunctionID: uint32)
	{.noconv, importc: "__cpuidex", header: "intrin.h".}
	cpuidMSVC(addr result, eax, ecx)
	else:
	# Note: https://bugs.llvm.org/show_bug.cgi?id=17907
	# AddressSanitizer + -mstackrealign might not respect RBX clobbers.
	asm """
	cpuid
	:"=a"(`result.eax`), "=b"(`result.ebx`), "=c"(`result.ecx`), "=d"(`result.edx`)
	:"a"(`eax`), "c"(`ecx`)"""

[mratsim]

It seems like the MacOS CI is now using ARM CPUs:

and the make_headers task assumes it is running on x86

  Executing task make_lib in /Users/runner/work/constantine/constantine/constantine/constantine.nimble
Compiling static library:  lib/libconstantine.a.arm
Compiling static library:  lib/libconstantine.a.x64
Compiling dynamic library: lib/libconstantine.dylib.arm
ld: warning: ignoring duplicate libraries: '-lm'
Compiling dynamic library: lib/libconstantine.dylib.x64
ld: warning: ignoring duplicate libraries: '-lm'
  Executing task make_headers in /Users/runner/work/constantine/constantine/constantine/constantine.nimble
/Users/runner/work/constantine/constantine/constantine/nimcache/libcurves_headers/@m..@sconstantine@splatforms@sisa@scpudetect_x86.nim.c:80:8: error: invalid output constraint '=a' in asm
      :"=a"(result.eax), "=b"(result.ebx), "=c"(result.ecx), "=d"(result.edx)
       ^

However building a fat binary for both x86 and ARM works well.

[mratsim]

Cross-compiling for Linux ARM64 on Linux x86 host works with Clang.

However looking at the error message we can see Nim Compiler version 1.6.21 [MacOSX: amd64]
but the host is actually arm64-apple-darwin23.4.0

So I suspect Nim is actually running through Rosetta and "thinks" it is on a x86 platform, which leads to this const X86 check being mistakenly true:

constantine/constantine/platforms/config.nim

Lines 12 to 13 in 976c8bb

	const GCC_Compatible* = defined(gcc) or defined(clang) or defined(llvm_gcc) or defined(icc)
	const X86* = defined(amd64) or defined(i386)