configure: better detect windows 'bitness' (WOW64)

Signed-off-by: Fedor Indutny <fedor@indutny.com>

diff --git a/configure b/configure
index daea8ca..c0a4ace 100755 (executable)
--- a/configure
+++ b/configure
@@ -402,7 +402,8 @@ def host_arch_cc():
 def host_arch_win():
   """Host architecture check using environ vars (better way to do this?)"""
 
-  arch = os.environ.get('PROCESSOR_ARCHITECTURE', 'x86')
+  observed_arch = os.environ.get('PROCESSOR_ARCHITECTURE', 'x86')
+  arch = os.environ.get('PROCESSOR_ARCHITEW6432', observed_arch)
 
   matchup = {
     'AMD64'  : 'x64',