Add scripts for crosscompiling the toolchain using an already built native toolchain

prepare-cross-toolchain.sh

@@ -0,0 +1,33 @@
+#!/bin/sh
+
+set -e
+
+if [ $# -lt 3 ]; then
+    echo $0 src dest arch
+    exit 1
+fi
+SRC="$1"
+DEST="$2"
+CROSS_ARCH="$3"
+
+: ${ARCHS:=${TOOLCHAIN_ARCHS-i686 x86_64 armv7 aarch64}}
+
+CLANG_VERSION=$(basename $(dirname $(dirname $(dirname $($SRC/bin/clang --print-libgcc-file-name -rtlib=compiler-rt)))))
+
+# If linked to a shared libc++/libunwind, we need to bundle those DLLs
+# in the bin directory.
+for i in libc++ libunwind; do
+    if [ -f $SRC/$CROSS_ARCH-w64-mingw32/bin/$i.dll ]; then
+        cp $SRC/$CROSS_ARCH-w64-mingw32/bin/$i.dll $DEST/bin
+    fi
+done
+
+cp -a $SRC/lib/clang/$CLANG_VERSION/lib $DEST/lib/clang/$CLANG_VERSION
+rm -rf $DEST/include
+cp -a $SRC/generic-w64-mingw32/include $DEST/include
+for arch in $ARCHS; do
+    mkdir -p $DEST/$arch-w64-mingw32
+    for subdir in bin lib; do
+        cp -a $SRC/$arch-w64-mingw32/$subdir $DEST/$arch-w64-mingw32
+    done
+done