sha2 fails to compile on windows w/ asm feature flag

[TheDan64]

Caused by:
  process didn't exit successfully: `C:\Users\dkolsoi\repos\oxidize\target\debug\build\sha2-asm-ef1bd78e3aeb1829\build-script-build` (exit code: 1)
  --- stdout
  TARGET = Some("x86_64-pc-windows-msvc")
  OPT_LEVEL = Some("0")
  HOST = Some("x86_64-pc-windows-msvc")
  CC_x86_64-pc-windows-msvc = None
  CC_x86_64_pc_windows_msvc = None
  HOST_CC = None
  CC = None
  CFLAGS_x86_64-pc-windows-msvc = None
  CFLAGS_x86_64_pc_windows_msvc = None
  HOST_CFLAGS = None
  CFLAGS = None
  CRATE_CC_NO_DEFAULTS = None
  CARGO_CFG_TARGET_FEATURE = Some("fxsr,sse,sse2")
  DEBUG = Some("true")
  running: "C:\\Program Files (x86)\\Microsoft Visual Studio\\2017\\BuildTools\\VC\\Tools\\MSVC\\14.16.27023\\bin\\HostX64\\x64\\cl.exe" "-nologo" "-MD" "-Z7" "-Brepro" "-W4" "-c" "-FoC:\\Users\\dkolsoi\\repos\\oxidize\\target\\debug\\build\\sha2-asm-e9bb7ad802cfe467\\out\\src/sha512_x64.o"
 "-c" "src/sha512_x64.S"
  cargo:warning=cl : Command line warning D9024 : unrecognized source file type 'src/sha512_x64.S', object file assumed
  cargo:warning=cl : Command line warning D9027 : source file 'src/sha512_x64.S' ignored
  cl : Command line warning D9021 : no action performed
  exit code: 0
  AR_x86_64-pc-windows-msvc = None
  AR_x86_64_pc_windows_msvc = None
  HOST_AR = None
  AR = None
  running: "C:\\Program Files (x86)\\Microsoft Visual Studio\\2017\\BuildTools\\VC\\Tools\\MSVC\\14.16.27023\\bin\\HostX64\\x64\\lib.exe" "-out:C:\\Users\\dkolsoi\\repos\\oxidize\\target\\debug\\build\\sha2-asm-e9bb7ad802cfe467\\out\\libsha512.a" "-nologo" "C:\\Users\\dkolsoi\\repos\\oxid
ize\\target\\debug\\build\\sha2-asm-e9bb7ad802cfe467\\out\\src/sha512_x64.o"
  LINK : fatal error LNK1181: cannot open input file 'C:\Users\dkolsoi\repos\oxidize\target\debug\build\sha2-asm-e9bb7ad802cfe467\out\src\sha512_x64.o'
  exit code: 1181

  --- stderr


  error occurred: Command "C:\\Program Files (x86)\\Microsoft Visual Studio\\2017\\BuildTools\\VC\\Tools\\MSVC\\14.16.27023\\bin\\HostX64\\x64\\lib.exe" "-out:C:\\Users\\dkolsoi\\repos\\oxidize\\target\\debug\\build\\sha2-asm-e9bb7ad802cfe467\\out\\libsha512.a" "-nologo" "C:\\Users\\dkolsoi
\\repos\\oxidize\\target\\debug\\build\\sha2-asm-e9bb7ad802cfe467\\out\\src/sha512_x64.o" with args "lib.exe" did not execute successfully (status code exit code: 1181).

But compiles fine without the asm flag

[tarcieri]

See RustCrypto/asm-hashes#17 and RustCrypto/asm-hashes#5

[newpavlov]

Going to close this issue in favor of the referenced ones.

[tarcieri]

Might be good to better document the asm feature. I can open a PR.