Adjust rebar.config to support rebar v2.0

- Include Windows preprocessor definitions that rebar is missing
- Minor changes to optimisation flags

rebar.config

@@ -13,7 +13,10 @@
 
     %% OS X Snow Leopard flags for 32-bit
     {"darwin10.*-32$", "CXXFLAGS", "-m32"},
-    {"darwin10.*-32$", "LDFLAGS", "-arch i386"}
+    {"darwin10.*-32$", "LDFLAGS", "-arch i386"},
+
+    %% This will merge into basho/rebar/rebar.config eventually
+    {"win32", "CFLAGS", "/Wall /DWIN32 /D_WINDOWS /D_WIN32 /DWINDOWS"}
 ]}.