Add build support for mingw32

[rharwood@redhat.com squashed commits, rewrote commit message, and added log
message when krb5-config isn't found]

gssapi/raw/python_gssapi.h

@@ -1,5 +1,7 @@
 #ifdef OSX_HAS_GSS_FRAMEWORK
 #include <GSS/GSS.h>
+#elif __MINGW32__
+#include <gss.h>
 #else
 #include <gssapi/gssapi.h>
 #endif

gssapi/raw/python_gssapi_ext.h

@@ -1,9 +1,13 @@
 #ifdef OSX_HAS_GSS_FRAMEWORK
 #include <GSS/GSS.h>
 #else
+#ifdef __MINGW32__
+#include <gss.h>
+#else
 #ifdef HAS_GSSAPI_EXT_H
 #include <gssapi/gssapi_ext.h>
 #else
 #include <gssapi/gssapi.h>
 #endif
 #endif
+#endif

gssapi/raw/python_gssapi_krb5.h

@@ -1,5 +1,7 @@
 #ifdef OSX_HAS_GSS_FRAMEWORK
 #include <GSS/gssapi_krb5.h>
+#elif __MINGW32__
+#include <gss.h>
 #else
 #include <gssapi/gssapi_krb5.h>
 #endif

setup.py

@@ -52,20 +52,29 @@ def _get_output(*args, **kwargs):
 if link_args is None:
     if osx_has_gss_framework:
         link_args = '-framework GSS'
+    elif os.environ.get('MINGW_PREFIX'):
+        link_args = '-lgss'
     else:
         link_args = get_output('krb5-config --libs gssapi')
 
 if compile_args is None:
     if osx_has_gss_framework:
         compile_args = '-framework GSS -DOSX_HAS_GSS_FRAMEWORK'
+    elif os.environ.get('MINGW_PREFIX'):
+        compile_args = '-fPIC'
     else:
         compile_args = get_output('krb5-config --cflags gssapi')
 
 link_args = link_args.split()
 compile_args = compile_args.split()
 
 # add in the extra workarounds for different include structures
-prefix = get_output('krb5-config gssapi --prefix')
+try:
+    prefix = get_output('krb5-config gssapi --prefix')
+except Exception:
+    print("WARNING: couldn't find krb5-config; assuming prefix of %s"
+          % str(sys.prefix))
+    prefix = sys.prefix
 gssapi_ext_h = os.path.join(prefix, 'include/gssapi/gssapi_ext.h')
 if os.path.exists(gssapi_ext_h):
     compile_args.append("-DHAS_GSSAPI_EXT_H")
@@ -85,6 +94,8 @@ def _get_output(*args, **kwargs):
     main_path = ""
     if main_lib is None and osx_has_gss_framework:
         main_lib = ctypes.util.find_library('GSS')
+    elif os.environ.get('MINGW_PREFIX'):
+        main_lib = os.environ.get('MINGW_PREFIX')+'/bin/libgss-3.dll'
     elif main_lib is None:
         for opt in link_args:
             if opt.startswith('-lgssapi'):