bootstrap: export _PW_ACTUAL_ENVIRONMENT_ROOT

This is currently used for arduino builds to find where cipd bin folder
is located. Relevant line:
https://cs.opensource.google/pigweed/pigweed/+/master:pw_arduino_build/arduino.gni;l=40

Change-Id: Iba38efdea16be06c84640d68c71bbca139bb884f
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/21920
Reviewed-by: Rob Mohr <mohrr@google.com>
Commit-Queue: Anthony DiGirolamo <tonymd@google.com>
diff --git a/bootstrap.sh b/bootstrap.sh
index 6089f47..6d00895 100644
--- a/bootstrap.sh
+++ b/bootstrap.sh
@@ -74,6 +74,7 @@
 pw_eval_sourced "$_pw_sourced"
 pw_check_root "$PW_ROOT"
 _PW_ACTUAL_ENVIRONMENT_ROOT="$(pw_get_env_root)"
+export _PW_ACTUAL_ENVIRONMENT_ROOT
 SETUP_SH="$_PW_ACTUAL_ENVIRONMENT_ROOT/activate.sh"
 
 # Downstream projects may wish to set PW_BANNER_FUNC to a function that prints