disable querying git in benchmarking code

This benchmarking library will try to query git for the current SHA, and this
code is called even if llvm-libc's benchmarks are disabled.

Querying git modifies `index.lock` files, which makes Portage's sandbox unhappy.
Manually set a failure value here instead.

patch.cherry: false
patch.platforms: chromiumos
patch.version_range.from: 0
patch.version_range.until: null

Change-Id: I66e96c7d72961d53b3763d66d766fe5e119823c7

third-party/benchmark/CMakeLists.txt

diff --git a/third-party/benchmark/CMakeLists.txt b/third-party/benchmark/CMakeLists.txt
index 8af4940..71e5603 100644
--- a/third-party/benchmark/CMakeLists.txt
+++ b/third-party/benchmark/CMakeLists.txt
@@ -105,8 +105,9 @@
 
 
 # Read the git tags to determine the project version
-include(GetGitVersion)
-get_git_version(GIT_VERSION)
+#include(GetGitVersion)
+#get_git_version(GIT_VERSION)
+set(GIT_VERSION "0.0.0")
 
 # If no git version can be determined, use the version
 # from the project() command