Fix linking of static libmagic with mingw

ac/gnurx.m4

@@ -0,0 +1,11 @@
+dnl
+dnl Check for libgnurx on mingw
+dnl
+if test "x$ac_cv_mingw32" = "xyes"; then
+  AC_CHECK_LIB(gnurx, regexec, [ gnurx_found=yes ], [ gnurx_found=no ])
+fi
+
+if test "x$gnurx_found" = xyes ; then
+  GNURX_LIBS=-lgnurx
+fi
+AC_SUBST(GNURX_LIBS)

ac/magic.m4

@@ -1,15 +1,18 @@
 dnl
 dnl Check for libmagic
 dnl
-AC_CHECK_LIB(magic, magic_open,
-             [ MAGIC_LIBS="-lmagic -lz"
-               magic_found=yes ],
-             [ magic_found=no ],
-             -lz)
+
+magic_mingw_libs=""
+if test "x$ac_cv_mingw32" = "xyes"; then
+  magic_mingw_libs="-lshlwapi"
+fi
+
+AC_CHECK_LIB(magic, magic_open, [ magic_found=yes ], [ magic_found=no ], [-lz $GNURX_LIBS $magic_mingw_libs])
 
 if test "x$magic_found" = "xyes" ; then
   AC_CHECK_HEADERS([magic.h])
   if test "x$ac_cv_header_magic_h" = "xyes" ; then
+    MAGIC_LIBS="-lmagic -lz $GNURX_LIBS $magic_mingw_libs"
     opt_features_yes="$opt_features_yes\n   * libMagic file type detection"
   else
     opt_features_no="$opt_features_no\n   * libMagic file type detection"

configure.in

@@ -40,6 +40,7 @@ m4_include(ac/lzo.m4)
 m4_include(ac/bz.m4)
 m4_include(ac/wxwidgets.m4)
 m4_include(ac/qt4.m4)
+m4_include(ac/gnurx.m4)
 m4_include(ac/magic.m4)
 m4_include(ac/curl.m4)
 m4_include(ac/ax_boost_base.m4)