# File lib/mkmf.rb, line 937
def create_header(header = "extconf.h")
  message "creating %s\n", header
  sym = header.tr("a-z./\055", "A-Z___")
  hdr = ["#ifndef #{sym}\n#define #{sym}\n"]
  for line in $defs
    case line
    when /^-D([^=]+)(?:=(.*))?/
      hdr << "#define #$1 #{$2 ? Shellwords.shellwords($2)[0] : 1}\n"
    when /^-U(.*)/
      hdr << "#undef #$1\n"
    end
  end
  hdr << "#endif\n"
  hdr = hdr.join
  unless (IO.read(header) == hdr rescue false)
    open(header, "w") do |hfile|
      hfile.write(hdr)
    end
  end
  $extconf_h = header
end