Split the building of the toolchain into individual shellscripts

This simplifies building the toolchain outside of docker.

install-wrappers.sh

@@ -0,0 +1,20 @@
+#!/bin/sh
+
+set -e
+
+if [ $# -lt 1 ]; then
+    echo $0 dest
+    exit 1
+fi
+PREFIX="$1"
+
+: ${ARCHS:=${TOOLCHAIN_ARCHS-i686 x86_64 armv7 aarch64}}
+
+mkdir -p $PREFIX/bin
+cp wrappers/clang-target-wrapper $PREFIX/bin
+cd $PREFIX/bin
+for arch in $ARCHS; do
+    for exec in clang clang++; do
+        ln -sf clang-target-wrapper $arch-w64-mingw32-$exec
+    done
+done