Fix using build machine compiler flags rather than target

This fix uses the 'setup.cfg' file used by setuptools to define parameters
for cross-compiling.

The reason for using this config file is that command-line parameters can't
be passed to setup.py, as the command-line is ideally opaque to the
installer. 'setup.cfg' was added to setuptools as a useful middle-ground
between modifying 'setup.py' and the command line. Now, build systems can
modify a config file instead of the source directly.

config.py

@@ -0,0 +1,70 @@
+#
+#    ICRAR - International Centre for Radio Astronomy Research
+#    (c) UWA - The University of Western Australia, 2014
+#    Copyright by UWA (in the framework of the ICRAR)
+#    All rights reserved
+#
+#    This library is free software; you can redistribute it and/or
+#    modify it under the terms of the GNU Lesser General Public
+#    License as published by the Free Software Foundation; either
+#    version 2.1 of the License, or (at your option) any later version.
+#
+#    This library is distributed in the hope that it will be useful,
+#    but WITHOUT ANY WARRANTY; without even the implied warranty of
+#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+#    Lesser General Public License for more details.
+#
+#    You should have received a copy of the GNU Lesser General Public
+#    License along with this library; if not, write to the Free Software
+#    Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+#    MA 02111-1307  USA
+#
+
+try:
+    import configparser
+except ImportError:
+    # Python 2 compatibility
+    import ConfigParser as configparser
+
+class setup_config(object):
+    """
+    Class to obtain configuration provided by the setup.cfg file used by
+    setuptools.
+    """
+
+    # Setuptools configuration file
+    SETUPTOOLS_CONFIG_FILE = 'setup.cfg'
+
+    # Cross-compiling section
+    BUILD_SECTION_NAME = 'build_info'
+
+    # Key name for specifying the target machine
+    MACHINE_KEY = 'machine'
+
+    def __init__(self):
+        """Initialize the configuration object"""
+        self._metadata = self._metadata_from_setupcfg(self.BUILD_SECTION_NAME)
+
+    def machine(self):
+        """Return the target machine name, or None if unknown"""
+        return self._get_cfg_value(self.MACHINE_KEY)
+
+    def _get_cfg_value(self, key):
+        """
+        Get a value associated with a key in the build section. Returns the
+        value, or None if unknown.
+        """
+        return self._metadata.get(key, None)
+
+    @classmethod
+    def _metadata_from_setupcfg(cls, section_name):
+        """Read the section of setup.cfg and return it as a dict"""
+        cfgparser = configparser.ConfigParser()
+        cfgparser.read(cls._get_cfg_filename())
+
+        return dict(cfgparser.items(section_name))
+
+    @classmethod
+    def _get_cfg_filename(cls):
+        """Get the file name of the setuptools cfg file"""
+        return cls.SETUPTOOLS_CONFIG_FILE

setup.cfg

@@ -0,0 +1,6 @@
+# Cross-compiling configuration interface
+[build_info]
+
+# If cross-compiling, uncomment this and set it to the target machine name
+# (e.g. output of uname -m). If unset, the host machine type will be detected.
+#machine = x86_64

setup.py

@@ -19,6 +19,8 @@
 #    Foundation, Inc., 59 Temple Place, Suite 330, Boston,
 #    MA 02111-1307  USA
 #
+from config import setup_config
+
 import glob
 import platform
 
@@ -33,7 +35,14 @@
                        language='c',
                        sources=['_crc32c.c', 'crc32c_sw.c'],
                        include_dirs=['.'])
-is_intel = platform.machine() in ['x86_64', 'AMD64']
+
+config = setup_config()
+
+machine = config.machine()
+if not machine:
+    machine = platform.machine()
+
+is_intel = machine in ['x86_64', 'AMD64']
 
 def get_extra_compile_args():
     # msvc is treated specially; otherwise we assume it's a unix compiler