Add --enable-auto-image-base for building mingw32 & cygwin DLLs

Originally committed as revision 9075 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -1167,7 +1167,7 @@ case $targetos in
     SLIBNAME_WITH_MAJOR='$(SLIBPREF)$(NAME)-$(LIBMAJOR)$(SLIBSUF)'
     SLIB_EXTRA_CMD="-lib /machine:i386 /def:\$(@:${SLIBSUF}=.def)"
     SLIB_INSTALL_EXTRA_CMD="-install -m 644 \$(SLIBNAME_WITH_MAJOR:\$(SLIBSUF)=.lib) \"\$(shlibdir)/\$(SLIBNAME_WITH_MAJOR:\$(SLIBSUF)=.lib)\""
-    SHFLAGS="-shared -Wl,--output-def,\$(@:${SLIBSUF}=.def),--out-implib,lib\$(SLIBNAME:\$(SLIBSUF)=.dll.a) -Wl,--enable-runtime-pseudo-reloc"
+    SHFLAGS="-shared -Wl,--output-def,\$(@:${SLIBSUF}=.def),--out-implib,lib\$(SLIBNAME:\$(SLIBSUF)=.dll.a) -Wl,--enable-runtime-pseudo-reloc -Wl,--enable-auto-image-base"
     enabled network && add_extralibs -lws2_32
     ;;
   cygwin*)
@@ -1182,7 +1182,7 @@ case $targetos in
     SLIBSUF=".dll"
     SLIBNAME_WITH_VERSION='$(SLIBPREF)$(NAME)-$(LIBVERSION)$(SLIBSUF)'
     SLIBNAME_WITH_MAJOR='$(SLIBPREF)$(NAME)-$(LIBMAJOR)$(SLIBSUF)'
-    SHFLAGS='-shared -Wl,--out-implib=lib$(NAME).dll.a'
+    SHFLAGS='-shared -Wl,--out-implib=lib$(NAME).dll.a -Wl,--enable-auto-image-base'
     ;;
   linux)
     LDLATEFLAGS="-Wl,--as-needed $LDLATEFLAGS"