docs/releasing: build test the scons/mingw build

We had multiple cases in the past where files used only by the
Scons/MinGW/Windows build were missing.

Avoid such instances and add a step to catch them early.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>
diff --git a/docs/releasing.html b/docs/releasing.html
index 09ef4ac..ec1baee 100644
--- a/docs/releasing.html
+++ b/docs/releasing.html
@@ -343,11 +343,17 @@
 
 	$__mesa_root/autogen.sh --enable-llvm-shared-libs &amp;&amp; make -j2 distcheck
 
-	# Build check the tarballs (scons)
-	tar -xaf mesa-$__version.tar.xz &amp;&amp; cd mesa-$__version &amp;&amp; scons &amp;&amp; cd ..
+	# Build check the tarballs (scons, linux)
+	tar -xaf mesa-$__version.tar.xz &amp;&amp; cd mesa-$__version
+	scons
+	cd .. &amp;&amp; rm -rf mesa-$__version
+
+	# Build check the tarballs (scons, windows/mingw)
+	tar -xaf mesa-$__version.tar.xz &amp;&amp; cd mesa-$__version
+	scons platform=windows toolchain=crossmingw
+	cd .. &amp;&amp; rm -rf mesa-$__version
 
 	# Test the automake binaries
-	rm -rf mesa-$__version
 	tar -xaf mesa-$__version.tar.xz &amp;&amp; cd mesa-$__version
 	./configure \
 		--with-dri-drivers=i965,swrast \