Only define _WIN32_WINNT=0x0501 if $target_os = "mingw32".

If compatibility with pre-XP versions is desired, use
--target-os=mingw32-prexp
Patch by Martin Storsjö <martin at martin dot st>.

Originally committed as revision 21441 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -2075,8 +2075,11 @@ case $target_os in
             { check_cflags -mdynamic-no-pic && add_asflags -mdynamic-no-pic; }
         ;;
     mingw32*)
-        # Only WinXP or greater are supported
-        add_cflags -D_WIN32_WINNT=0x0501
+        # Adding _WIN32_WINNT=0x0501 makes functions that require
+        # XP visible and thus may make it binary incompatible with
+        # earlier versions. Set --target-os=mingw32-prexp if this
+        # isn't desired.
+        test $target_os = "mingw32" && add_cflags -D_WIN32_WINNT=0x0501
         if test $target_os = "mingw32ce"; then
             disable network
         else

doc/general.texi

@@ -998,8 +998,8 @@ and for a build with shared libraries
 @subsection Win9x/Win2000 support
 
 FFmpeg is built by default for Windows XP and above. To run it on any Windows
-version prior to XP, you may have to disable network support. Additionally, for
-Windows 98/Me you must install KernelEx from:
+version prior to XP, you must use @code{--target-os=mingw32-prexp}.
+Additionally, for Windows 98/Me you must install KernelEx from:
 http://sourceforge.net/projects/kernelex/
 
 @section BeOS