configure.ac: Only enforce WIN32_WINNT when it's missing

Makefile.am

@@ -6,9 +6,6 @@ AM_CPPFLAGS = -Wall -Wsign-compare -Wextra -Wstrict-aliasing -Wstrict-overflow \
 			  -pipe
 
 MEDIALIB_CPPFLAGS = $(AM_CPPFLAGS) -I$(top_srcdir)/include -I$(top_srcdir)/src
-if HAVE_WIN32
-MEDIALIB_CPPFLAGS += -D_WIN32_WINNT=0x600
-endif
 
 libmedialibrary_ladir = $(includedir)/medialibrary
 

configure.ac

@@ -265,6 +265,12 @@ AS_IF([test "$SYS" = linux],[
 ])
 AM_CONDITIONAL(HAVE_ANDROID, test "${HAVE_ANDROID}" = "1")
 
+AS_IF([test "$SYS" = mingw32],[
+    AC_CHECK_DECL(_WIN32_WINNT,,
+        AC_DEFINE([_WIN32_WINNT], 0x600, [Enforce a specific windows SDK version])
+    )
+])
+
 PKG_CHECK_MODULES(SQLITE, sqlite3)
 PKG_CHECK_MODULES(VLC, libvlc >= 3.0)
 PKG_CHECK_MODULES(VLCPP, libvlcpp,