Get Bogo test working on M1 ("Apple Silicon") macOS Big Sur.

Fix the "build bogo_shim if it doesn't exist" logic; it was broken even
on Linux as newer versions of Rust don't allow `--features` to be used
at workspace level.

I had to bootstrap Go on a Linux machine using the procedure at
golang/go#42684 (comment):
```
git clone https://go.googlesource.com/go
cd go
git fetch https://go.googlesource.com/go refs/changes/58/272258/1 && git checkout FETCH_HEAD
cd src
GOOS=darwin GOARCH=arm64 ./bootstrap.bash
```

This version of Go required me to have a go.mod file. Change the way Bogo is
downloaded from BoringSSL's repo to get this to work. The script tries to use
sparse checkouts and a single-revision checkout but it is still slow so maybe
one or both of those things aren't working as I expect.

In particular, avoid `wget` since my Mac doesn't have `wget` available.

Remove two of the patches to Bogo that seem to not be necessary if using a
newer version of Go. Patch the remaining patch to work with the new directory
structure.

I verified that ./runme runs the tests and spits out "PASS" at the end on both macOS
and Linux.

bogo/fetch-and-build

@@ -1,19 +1,22 @@
-#!/bin/sh
+#!/bin/bash
 
 set -ex
 
+mkdir bogo
+pushd bogo
+
+git init
+cat << EOF > .git/info/sparse-checkout
+go.mod
+ssl/test/runner
+util/testresult
+EOF
+
 # a known-good commit
 COMMIT=47a6f5b4bf4d7acd8d5f7d43cb9c94335cec1c60
-
-rm -f runner.tar.gz testresult.tar.gz
-wget https://boringssl.googlesource.com/boringssl/+archive/$COMMIT/ssl/test/runner.tar.gz
-wget https://boringssl.googlesource.com/boringssl/+archive/$COMMIT/util/testresult.tar.gz
-mkdir -p bogo
-cd bogo/
-mkdir -p testresult
-tar -xzf ../runner.tar.gz
-( cd testresult && tar -xzf ../../testresult.tar.gz )
+git fetch https://boringssl.googlesource.com/boringssl $COMMIT
+git checkout $COMMIT
 patch -p1 < ../patches/testerrormap.diff
-patch -p1 < ../patches/go-1.13-breakage.diff
-patch -p1 < ../patches/vendor.diff
-go test -c
+(cd ssl/test/runner && go test -c)
+
+popd

bogo/patches/testerrormap.diff

@@ -1,6 +1,6 @@
-diff -u original/runner.go bogo/runner.go
---- original/runner.go	2018-09-13 21:07:29.000000000 +0100
-+++ bogo/runner.go	2019-01-20 11:51:00.705040230 +0000
+diff -u original/ssl/test/runner/runner.go bogo/ssl/test/runner/runner.go
+--- original/ssl/test/runner/runner.go	2018-09-13 21:07:29.000000000 +0100
++++ bogo/ssl/test/runner/runner.go	2019-01-20 11:51:00.705040230 +0000
 @@ -84,6 +84,14 @@
  	// like “SSL_ERROR_NO_CYPHER_OVERLAP”.
  	ErrorMap map[string]string

bogo/runme

@@ -6,7 +6,7 @@
 set -xe
 
 if [ ! -e ../target/debug/examples/bogo_shim ] ; then
-  cargo test --no-run --features dangerous_configuration,quic
+  (cd ../rustls && cargo build --example bogo_shim --features dangerous_configuration,quic)
 fi
 
 if [ ! -e bogo/ ] ; then
@@ -17,7 +17,7 @@ fi
 # Best effort on OS-X
 case $OSTYPE in darwin*) set +e ;; esac
 
-( cd bogo && ./bogo.test -shim-path ../../target/debug/examples/bogo_shim \
-     -shim-config ../config.json \
+( cd bogo/ssl/test/runner && ./runner.test -shim-path ../../../../../target/debug/examples/bogo_shim \
+     -shim-config ../../../../config.json \
      -pipe -allow-unimplemented )
 true