MinGW: No longer ignore expat_config.h

Previously, "#define XML_CONTEXT_BYTES 1024" from winconfig.h
would render --disable-xml-context ineffective.

expat/lib/winconfig.h

@@ -17,6 +17,12 @@
 #include <memory.h>
 #include <string.h>
 
+
+#if defined(HAVE_EXPAT_CONFIG_H)  /* e.g. MinGW */
+# include <expat_config.h>
+#else  /* !defined(HAVE_EXPAT_CONFIG_H) */
+
+
 #define XML_NS 1
 #define XML_DTD 1
 #define XML_CONTEXT_BYTES 1024
@@ -27,4 +33,8 @@
 /* Windows has memmove() available. */
 #define HAVE_MEMMOVE
 
+
+#endif /* !defined(HAVE_EXPAT_CONFIG_H) */
+
+
 #endif /* ndef WINCONFIG_H */