The crate doesn't build on Windows ARM64

[ssg]

The build fails on Windows ARM64 because of ring package (possibly, it won't build on x86 either):

error: failed to run custom build command for `ring v0.16.20`

  --- stdout
  OPT_LEVEL = Some("0")
  TARGET = Some("aarch64-pc-windows-msvc")
  HOST = Some("aarch64-pc-windows-msvc")
  cargo:rerun-if-env-changed=CC_aarch64-pc-windows-msvc
  CC_aarch64-pc-windows-msvc = None
  cargo:rerun-if-env-changed=CC_aarch64_pc_windows_msvc
  CC_aarch64_pc_windows_msvc = None
  cargo:rerun-if-env-changed=HOST_CC
  HOST_CC = None
  cargo:rerun-if-env-changed=CC
  CC = None
  cargo:rerun-if-env-changed=CFLAGS_aarch64-pc-windows-msvc
  CFLAGS_aarch64-pc-windows-msvc = None
  cargo:rerun-if-env-changed=CFLAGS_aarch64_pc_windows_msvc
  CFLAGS_aarch64_pc_windows_msvc = None
  cargo:rerun-if-env-changed=HOST_CFLAGS
  HOST_CFLAGS = None
  cargo:rerun-if-env-changed=CFLAGS
  CFLAGS = None
  cargo:rerun-if-env-changed=CRATE_CC_NO_DEFAULTS
  CRATE_CC_NO_DEFAULTS = None
  CARGO_CFG_TARGET_FEATURE = Some("neon")
  DEBUG = Some("true")
  montgomery.c
  $HOME\.cargo\registry\src\github.com-1ecc6299db9ec823\ring-0.16.20\crypto\fipsmodule\bn\internal.h(191): error C2065: 'BN_ULLONG': undeclared identifier
  $HOME\.cargo\registry\src\github.com-1ecc6299db9ec823\ring-0.16.20\crypto\fipsmodule\bn\internal.h(191): error C2146: syntax error: missing ';' before identifier 'result'
  $HOME\.cargo\registry\src\github.com-1ecc6299db9ec823\ring-0.16.20\crypto\fipsmodule\bn\internal.h(191): warning C4555: result of expression not used
  $HOME\.cargo\registry\src\github.com-1ecc6299db9ec823\ring-0.16.20\crypto\fipsmodule\bn\internal.h(191): error C2065: 'result': undeclared identifier
  $HOME\.cargo\registry\src\github.com-1ecc6299db9ec823\ring-0.16.20\crypto\fipsmodule\bn\internal.h(191): error C2146: syntax error: missing ';' before identifier 'a'
  $HOME\.cargo\registry\src\github.com-1ecc6299db9ec823\ring-0.16.20\crypto\fipsmodule\bn\internal.h(191): warning C4552: '*': result of expression not used
  $HOME\.cargo\registry\src\github.com-1ecc6299db9ec823\ring-0.16.20\crypto\fipsmodule\bn\internal.h(192): error C2065: 'result': undeclared identifier
  $HOME\.cargo\registry\src\github.com-1ecc6299db9ec823\ring-0.16.20\crypto\fipsmodule\bn\internal.h(193): error C2065: 'result': undeclared identifier
  $HOME\.cargo\registry\src\github.com-1ecc6299db9ec823\ring-0.16.20\crypto\fipsmodule\bn\internal.h(193): warning C4293: '>>': shift count negative or too big, undefined behavior
  $HOME\.cargo\registry\src\github.com-1ecc6299db9ec823\ring-0.16.20\crypto\fipsmodule\bn\../../limbs/limbs.inl(38): warning C4163: '_addcarry_u64': not available as an intrinsic function
  $HOME\.cargo\registry\src\github.com-1ecc6299db9ec823\ring-0.16.20\crypto\fipsmodule\bn\../../limbs/limbs.inl(38): warning C4163: '_subborrow_u64': not available as an intrinsic function
  $HOME\.cargo\registry\src\github.com-1ecc6299db9ec823\ring-0.16.20\crypto\fipsmodule\bn\../../limbs/limbs.inl(62): warning C4013: '_addcarry_u64' undefined; assuming extern returning int
  $HOME\.cargo\registry\src\github.com-1ecc6299db9ec823\ring-0.16.20\crypto\fipsmodule\bn\../../limbs/limbs.inl(62): warning C4242: '=': conversion from 'int' to 'Carry', possible loss of data
  $HOME\.cargo\registry\src\github.com-1ecc6299db9ec823\ring-0.16.20\crypto\fipsmodule\bn\../../limbs/limbs.inl(76): warning C4242: '=': conversion from 'int' to 'Carry', possible loss of data
  $HOME\.cargo\registry\src\github.com-1ecc6299db9ec823\ring-0.16.20\crypto\fipsmodule\bn\../../limbs/limbs.inl(92): warning C4013: '_subborrow_u64' undefined; assuming extern returning int
  $HOME\.cargo\registry\src\github.com-1ecc6299db9ec823\ring-0.16.20\crypto\fipsmodule\bn\../../limbs/limbs.inl(92): warning C4242: '=': conversion from 'int' to 'Carry', possible loss of data
  $HOME\.cargo\registry\src\github.com-1ecc6299db9ec823\ring-0.16.20\crypto\fipsmodule\bn\../../limbs/limbs.inl(106): warning C4242: '=': conversion from 'int' to 'Carry', possible loss of data

[gyuho]

I do not have Window machine but we will look for an alternative crypto crate (e.g., similar to ring) to support Window builds. Thanks for the report.