Update the BoringSSL benchmark to install libdecrepit (#1505)

### Description of changes: 
BoringSSL does not install libdecrepit by default, so our benchmark
patches the file to install it to simplify our testing. They recently
moved this to sources.cmake and the top level CMakeList.txt in
google/boringssl@0cb032a.
This causes issues for CI which now doesn't install libdecrepit and then
fails to link the AES XTS implementation from libdecrepit. This change
updates that.

### Testing:
Ran locally

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license and the ISC license.

tests/ci/run_benchmark_build_tests.sh

@@ -66,7 +66,7 @@ function build_openssl {
 function build_boringssl {
   git clone --depth 1 https://github.com/google/boringssl.git "${scratch_folder}/boringssl"
   pushd "${scratch_folder}/boringssl"
-  echo "install_if_enabled(TARGETS decrepit EXPORT OpenSSLTargets ${INSTALL_DESTINATION_DEFAULT})" >> decrepit/CMakeLists.txt
+  echo "install_if_enabled(TARGETS decrepit EXPORT OpenSSLTargets ${INSTALL_DESTINATION_DEFAULT})" >> CMakeLists.txt
   cmake -GNinja \
       -DCMAKE_INSTALL_PREFIX="${install_dir}/boringssl" \
       -DCMAKE_BUILD_TYPE=RelWithDebInfo .