Split the building of the toolchain into individual shellscripts

This simplifies building the toolchain outside of docker.

build-all.sh

@@ -0,0 +1,15 @@
+#!/bin/sh
+
+set -e
+
+if [ $# -lt 1 ]; then
+    echo $0 dest
+    exit 1
+fi
+PREFIX="$1"
+
+./build-llvm.sh $PREFIX
+./install-wrappers.sh $PREFIX
+./build-mingw-w64.sh $PREFIX
+./build-compiler-rt.sh $PREFIX 6.0.0
+./build-libcxx.sh $PREFIX