test experimental:compiletimeFFI on windows

[timotheecour]

follows #10150 and the recently merged Araq/libffi#6 which adds win64 support for libffi

[ringabout]

• libffi needs a tag or nimble install a specific hash
• stderr not being able to be imported on windows

[timotheecour]

@xflywind

stderr not being able to be imported on windows

i had added nimEvalffiStderrWorkaround a while back to support openbsd; can you test if this change would make things work on windows:

when defined(openbsd):
=>
when defined(openbsd) or defined(windows):

(in tests/misc/trunner.nim)

?
thanks!

(in future work, this can be improved by using similar approach to proposal 5 from nim-lang/RFCs#205, shelling out to clang as discussed elsewhere)

[ringabout]

I'm not sure how to test it.

bin/nim_temp c -r -d:nimTrunnerFfi tests/misc/trunner

Hint: C:\Users\blue\Documents\GitHub\Nim\tests\misc\trunner.exe  [Exec]
trunner.nim(68)          trunner
assertions.nim(38)       failedAssertImpl
assertions.nim(28)       raiseAssert
fatal.nim(53)            sysFatal
Error: unhandled exception: trunner.nim(68, 14) `output ==
    fmt"""{prefix}foo
foo:100
foo:101
foo:102:103
foo:102:103:104
foo:0.03:asdf:103:105
ret=[s1:foobar s2:foobar age:25 pi:3.14]
"""` MulCmp_352321691
MulCmp_352321691
MulCmp_352321690
foo
foo:100
foo:101
foo:102:103
foo:102:103:104
foo:0.03:asdf:103:105
ret=[s1:foobar s2:foobar age:25 pi:3.14]
 [AssertionDefect]
Error: execution of an external program failed: 'C:\Users\blue\Documents\GitHub\Nim\tests\misc\trunner.exe '
Traceback (most recent call last)
C:\Users\blue\Documents\GitHub\Nim\compiler\nim.nim(138) nim
C:\Users\blue\Documents\GitHub\Nim\compiler\nim.nim(119) handleCmdLine
C:\Users\blue\Documents\GitHub\Nim\compiler\extccomp.nim(403) execExternalProgram
C:\Users\blue\Documents\GitHub\Nim\compiler\msgs.nim(561) liMessage
C:\Users\blue\Documents\GitHub\Nim\compiler\msgs.nim(421) handleError
C:\Users\blue\Documents\GitHub\Nim\compiler\msgs.nim(402) quit

[timotheecour]

CI fails with:
2021-08-24T18:55:03.1470079Z could not load: C:\Users\VssAdministrator.nimble\pkgs\libffi-#153322d744666b312dd04b5cbd4e2444415e2260\libs\win64\libffi-7.dll

help welcome to figure out how to add libffi-7.dll for windows

how would i install libffi-7.dll dependency on windows, and in particular in CI?
CI uses nimInternalInstallDepsWindows; i'm assuming libffi-7.dll should be added to https://nim-lang.org/download/dlls.zip in the future but what can i do in the meantime (which is a necessary step before modifying dlls.zip anyways)
there's also https://sourceware.org/libffi/ but it mentions libffi-3.4.2, not libffi-7.dll; i'm not a windows user so I'm kind of in the dark here...

[ringabout]

stdout/stdin/stderr is defined as a macro in msvcrt.dll, so it doesn't work with importc.

[ringabout]

Like https://github.com/NVIDIA/winex_lgpl/blob/e06590034b384162c5fdb601a453de65898f2020/winex/include/msvcrt/stdio.h#L110