Bootstrap: fallback detection of Windows

src/bootstrap/bootstrap.py

@@ -184,6 +184,7 @@ def default_build_triple():
  ostype = require(["uname", "-s"], exit=required)
  cputype = require(['uname', '-m'], exit=required)
 
+ # If we do not have `uname`, assume Windows.
  if ostype is None or cputype is None:
  return 'x86_64-pc-windows-msvc'
 
@@ -236,6 +237,11 @@ def default_build_triple():
  if ostype.endswith('WOW64'):
  cputype = 'x86_64'
  ostype = 'pc-windows-gnu'
+ elif sys.platform == 'win32':
+ # Some Windows platforms might have a `uname` command that returns a
+ # non-standard string (e.g. gnuwin32 tools returns `windows32`). In
+ # these cases, fall back to using sys.platform.
+ return 'x86_64-pc-windows-msvc'
  else:
  err = "unknown OS type: {}".format(ostype)
  sys.exit(err)