the last parameter of XChangeProperty is the number of elements.. and when the element format is 32.. the element is "long" so we have 5 long elements here.

Yes this seems confusing as on mac+linux Long is either 32 or 64bits depending on the architecture, but this is how the X11 protocol is defined. Thus 5 is the correct value for the nelts here.  Not 5 or 10 depending on the architecture.

More info on the confusion https://bugs.freedesktop.org/show_bug.cgi?id=16802

build-scripts/emscripten-buildbot.sh

@@ -0,0 +1,72 @@
+#!/bin/bash
+
+SDKDIR="/emsdk_portable"
+ENVSCRIPT="$SDKDIR/emsdk_env.sh"
+if [ ! -f "$ENVSCRIPT" ]; then
+   echo "ERROR: This script expects the Emscripten SDK to be in '$SDKDIR'." 1>&2
+   exit 1
+fi
+
+TARBALL="$1"
+if [ -z $1 ]; then
+    TARBALL=sdl-emscripten.tar.xz
+fi
+
+cd `dirname "$0"`
+cd ..
+SDLBASE=`pwd`
+
+if [ -z "$MAKE" ]; then
+    OSTYPE=`uname -s`
+    if [ "$OSTYPE" == "Linux" ]; then
+        NCPU=`cat /proc/cpuinfo |grep vendor_id |wc -l`
+        let NCPU=$NCPU+1
+    elif [ "$OSTYPE" = "Darwin" ]; then
+        NCPU=`sysctl -n hw.ncpu`
+    elif [ "$OSTYPE" = "SunOS" ]; then
+        NCPU=`/usr/sbin/psrinfo |wc -l |sed -e 's/^ *//g;s/ *$//g'`
+    else
+        NCPU=1
+    fi
+
+    if [ -z "$NCPU" ]; then
+        NCPU=1
+    elif [ "$NCPU" = "0" ]; then
+        NCPU=1
+    fi
+
+    MAKE="make -j$NCPU"
+fi
+
+echo "\$MAKE is '$MAKE'"
+
+echo "Setting up Emscripten SDK environment..."
+source "$ENVSCRIPT"
+
+echo "Setting up..."
+set -x
+cd "$SDLBASE"
+rm -rf buildbot
+mkdir buildbot
+pushd buildbot
+
+echo "Configuring..."
+emconfigure ../configure --host=asmjs-unknown-emscripten --disable-assembly --disable-threads --enable-cpuinfo=false CFLAGS="-O2 -Wno-warn-absolute-paths -Wdeclaration-after-statement -Werror=declaration-after-statement" --prefix="$PWD/emscripten-sdl2-installed"
+
+echo "Building..."
+emmake $MAKE
+
+echo "Moving things around..."
+emmake $MAKE install
+# Fix up a few things to a real install path
+perl -w -pi -e "s#$PWD/emscripten-sdl2-installed#/usr/local#g;" ./emscripten-sdl2-installed/lib/libSDL2.la ./emscripten-sdl2-installed/lib/pkgconfig/sdl2.pc ./emscripten-sdl2-installed/bin/sdl2-config
+mkdir -p ./usr
+mv ./emscripten-sdl2-installed ./usr/local
+popd
+tar -cJvvf $TARBALL -C buildbot usr
+rm -rf buildbot
+
+exit 0
+
+# end of emscripten-buildbot.sh ...
+