Add SymEngine build

This should let us do symbolic manipulation in C++ for the swerve plant
a lot more efficiently.

Change-Id: I9491b32b2a8357effb36b4a15d52c71d55945997
Signed-off-by: Austin Schuh <austin.linux@gmail.com>
diff --git a/tools/ci/buildkite.yaml b/tools/ci/buildkite.yaml
index 7b17c8a..be3cb07 100644
--- a/tools/ci/buildkite.yaml
+++ b/tools/ci/buildkite.yaml
@@ -1,7 +1,7 @@
 env:
   STARTUP: --max_idle_secs=0
   COMMON: -c opt --stamp=no --curses=yes --symlink_prefix=/ --remote_cache=grpc://data-fast:9092 --repo_env=FRC971_RUNNING_IN_CI=1 --repository_cache=~/.cache/bazel_repository --experimental_repository_cache_hardlinks=true
-  TARGETS: //... @com_github_google_glog//... @com_google_ceres_solver//... @com_github_rawrtc_rawrtc//... @com_google_googletest//...
+  TARGETS: //... @com_github_google_glog//... @com_google_ceres_solver//... @com_github_rawrtc_rawrtc//... @com_google_googletest//... @symengine//...
   M4F_TARGETS: //...
   RP2040_TARGETS: //...
   # Sanity check that we are able to build the y2020 roborio code, which confirms