setup: don't fail when Python doesn't have the cygwinccompiler package

Some Python installations like the ones available from the optware
project
for the Synology DiskStation NASes don't have that package, which means
running the setup script will crash and exit right away. Instead, we now
just use an empty/fake class for the HackedMingw32CCompiler, which we
likely won't use anyway.

setup.py

@@ -76,7 +76,7 b' from distutils.command.build_py import b'
 from distutils.command.install_lib import install_lib
 from distutils.command.install_scripts import install_scripts
 from distutils.spawn import spawn, find_executable
-from distutils import cygwinccompiler, file_util
+from distutils import file_util
 from distutils.errors import CCompilerError, DistutilsExecError
 from distutils.sysconfig import get_python_inc, get_config_var
 from distutils.version import StrictVersion
@@ -509,19 +509,28 b' else:'
                                 extra_link_args=osutil_ldflags,
                                 depends=common_depends))
 
-# the -mno-cygwin option has been deprecated for years
-Mingw32CCompiler = cygwinccompiler.Mingw32CCompiler
+try:
+    from distutils import cygwinccompiler
+
+    # the -mno-cygwin option has been deprecated for years
+    compiler = cygwinccompiler.Mingw32CCompiler
 
-class HackedMingw32CCompiler(cygwinccompiler.Mingw32CCompiler):
-    def __init__(self, *args, **kwargs):
-        Mingw32CCompiler.__init__(self, *args, **kwargs)
-        for i in 'compiler compiler_so linker_exe linker_so'.split():
-            try:
-                getattr(self, i).remove('-mno-cygwin')
-            except ValueError:
-                pass
+    class HackedMingw32CCompiler(cygwinccompiler.Mingw32CCompiler):
+        def __init__(self, *args, **kwargs):
+            compiler.__init__(self, *args, **kwargs)
+            for i in 'compiler compiler_so linker_exe linker_so'.split():
+                try:
+                    getattr(self, i).remove('-mno-cygwin')
+                except ValueError:
+                    pass
 
-cygwinccompiler.Mingw32CCompiler = HackedMingw32CCompiler
+    cygwinccompiler.Mingw32CCompiler = HackedMingw32CCompiler
+except ImportError:
+    # the cygwinccompiler package is not available on some Python
+    # distributions like the ones from the optware project for Synology
+    # DiskStation boxes
+    class HackedMingw32CCompiler(object):
+        pass
 
 packagedata = {'mercurial': ['locale/*/LC_MESSAGES/hg.mo',
                              'help/*.txt',