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/templates/target.user.j2

@@ -3,10 +3,10 @@
 {% block binaries %}
 cc = ${srcroot}/sysroot/bin/clang
 cxx = ${srcroot}/sysroot/bin/clang++
-ld = ${srcroot}/sysroot/bin/x86_64-elf-ld
-ar = ${srcroot}/sysroot/bin/x86_64-elf-ar
+ld = ${srcroot}/sysroot/bin/ld.lld
+ar = ${srcroot}/sysroot/bin/ar
 nasm = ${srcroot}/sysroot/bin/nasm
-objcopy = ${srcroot}/sysroot/bin/x86_64-elf-objcopy
+objcopy = ${srcroot}/sysroot/bin/objcopy
 {% endblock %}
 
 {% block variables %}
@@ -35,7 +35,6 @@ ldflags = $ldflags $
     -nostdlib $
     -znocombreloc $
     -Bsymbolic $
-    -nostartfiles $
     -Bstatic $
     --sysroot="${srcroot}/sysroot" $
 	-L "${srcroot}/sysroot/lib" $