Fails to cross-compile from linux to pc-windows-gnu

[dtolnay]

Official Windows documentation refers to it variously as Basetsd.h (https://docs.microsoft.com/en-us/windows/win32/winprog64/the-tools#include-files) and BaseTsd.h (https://docs.microsoft.com/en-us/windows/win32/winprog/windows-data-types) but it appears the actual file they ship is basetsd.h. As reported by jebrosen in discord:

the file is actually at Program Files (x86)/Windows Kits/10/Include/10.0.18362.0/shared/basetsd.h (lowercase) on my windows install. And of course windows being case-insensitive you probably wouldn't ever notice this except in cross-compilation

When cross compiling or compiling from a case sensitive filesystem, it fails to find out current import of BaseTsd.h added in #97.

The following warnings were emitted during compilation:

warning: In file included from src/cxx.cc:1:
warning: src/../include/cxx.h:14:10: fatal error: 'BaseTsd.h' file not found
warning: #include <BaseTsd.h>
warning:          ^~~~~~~~~~~
warning: 1 error generated.

error: failed to run custom build command for `cxx v0.4.4 (/git/cxx)`

Caused by:
  process didn't exit successfully: `/git/cxx/target/debug/build/cxx-d96d8bbe071f88b7/build-script-build` (exit code: 1)
  --- stdout
  TARGET = Some("x86_64-pc-windows-gnu")
  OPT_LEVEL = Some("0")
  HOST = Some("x86_64-unknown-linux-gnu")
  CXX_x86_64-pc-windows-gnu = None
  CXX_x86_64_pc_windows_gnu = None
  TARGET_CXX = None
  CXX = Some("clang++")
  CXXFLAGS_x86_64-pc-windows-gnu = None
  CXXFLAGS_x86_64_pc_windows_gnu = None
  TARGET_CXXFLAGS = None
  CXXFLAGS = None
  CRATE_CC_NO_DEFAULTS = None
  DEBUG = Some("true")
  CXX_x86_64-pc-windows-gnu = None
  CXX_x86_64_pc_windows_gnu = None
  TARGET_CXX = None
  CXX = Some("clang++")
  CXXFLAGS_x86_64-pc-windows-gnu = None
  CXXFLAGS_x86_64_pc_windows_gnu = None
  TARGET_CXXFLAGS = None
  CXXFLAGS = None
  CRATE_CC_NO_DEFAULTS = None
  running: "clang++" "-O0" "-ffunction-sections" "-fdata-sections" "-g" "-fno-omit-frame-pointer" "--target=x86_64-pc-windows-gnu" "-Wall" "-Wextra" "-std=c++11" "-o" "/git/cxx/target/x86_64-pc-windows-gnu/debug/build/cxx-e9cfa76dc60ab8d1/out/src/cxx.o" "-c" "src/cxx.cc"
  cargo:warning=In file included from src/cxx.cc:1:
  cargo:warning=src/../include/cxx.h:14:10: fatal error: 'BaseTsd.h' file not found
  cargo:warning=#include <BaseTsd.h>
  cargo:warning=         ^~~~~~~~~~~
  cargo:warning=1 error generated.
  exit code: 1

  --- stderr


  error occurred: Command "clang++" "-O0" "-ffunction-sections" "-fdata-sections" "-g" "-fno-omit-frame-pointer" "--target=x86_64-pc-windows-gnu" "-Wall" "-Wextra" "-std=c++11" "-o" "/git/cxx/target/x86_64-pc-windows-gnu/debug/build/cxx-e9cfa76dc60ab8d1/out/src/cxx.o" "-c" "src/cxx.cc" with args "clang++" did not execute successfully (status code exit code: 1).