Remove the _build directory before building protoc

php/generate_test_protos.sh

@@ -9,7 +9,10 @@ cd `dirname $0`
 if ../src/protoc --help > /dev/null; then
   PROTOC=src/protoc
 else
-  (cd .. && bazel build -c opt :protoc)
+  # Bazel seems to be creating a problematic symlink in
+  # _build/out/external/com_google_protobuf, so we remove the _build directory
+  # before building protoc.
+  (cd .. && rm -rf _build && bazel build -c opt :protoc)
   PROTOC=bazel-bin/protoc
 fi