Remove sysroot binutils dependency

* Link host-targeted binaries with lld
 * Add peru script for getting prebuilt sysroot
 * Add readme for prebuilt sysroots
 * Remove non-working build_sysroot_gcc.sh, rename clang version to just
   build_sysroot.sh

scripts/readme_for_prebuilt_sysroots.md

@@ -0,0 +1,47 @@
+# jsix OS sysroot
+
+This is a pre-built sysroot for building the jsix operating system kernel,
+bootloader, and utilities. This package is provided as a convenience, and
+contains software from the following repositories.
+
+## NASM, the Netwide Assembler
+
+As downloaded from [the NASM website][nasm] under the following license:
+
+    Copyright 1996-2010 the NASM Authors - All rights reserved.
+ 
+     Redistribution and use in source and binary forms, with or without
+     modification, are permitted provided that the following
+     conditions are met:
+ 
+     * Redistributions of source code must retain the above copyright
+       notice, this list of conditions and the following disclaimer.
+     * Redistributions in binary form must reproduce the above
+       copyright notice, this list of conditions and the following
+       disclaimer in the documentation and/or other materials provided
+       with the distribution.
+       
+       THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+       CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+       INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+       MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+       DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+       CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+       SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+       NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+       LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+       HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+       CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
+       OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
+       EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+[nasm]: https://www.nasm.us
+
+## The LLVM toolchain
+
+The LLVM sources as downloaded via git from [llvm.org][llvm] under the terms of
+the [Apache License v2.0][apache2], modified [as described here][llvmlic].
+
+[llvm]: https://llvm.org
+[apache2]: https://www.apache.org/licenses/LICENSE-2.0
+[llvmlic]: https://llvm.org/docs/DeveloperPolicy.html#new-llvm-project-license-framework