Fix compile warning for struct/class mismatch

./compile.sh is giving:

$ ./compile.sh build bazel-bin/src/bazel
🍃  Building Bazel with Bazel.
INFO: Found 1 target...
INFO: From Compiling src/main/cpp/blaze.cc:
In file included from src/main/cpp/blaze.cc:58:
./src/main/cpp/blaze_globals.h:42:1: warning: 'GlobalVariables' defined as a struct here but previously declared as a class [-Wmismatched-tags]
struct GlobalVariables {
^
./src/main/cpp/blaze_abrupt_exit.h:23:1: note: did you mean struct here?
class GlobalVariables;
^~~~~
struct
1 warning generated.

--
MOS_MIGRATED_REVID=111863702

1 files changed, 1 insertions, 1 deletions

diff --git a/src/main/cpp/blaze_abrupt_exit.h b/src/main/cpp/blaze_abrupt_exit.h
index 15b9fed641..df1422f9b2 100644
--- a/src/main/cpp/blaze_abrupt_exit.h
+++ b/src/main/cpp/blaze_abrupt_exit.h
@@ -20,7 +20,7 @@
 
 namespace blaze {
 
-class GlobalVariables;
+struct GlobalVariables;
 
 // Returns the exit code to use for when the Blaze server exits abruptly.
 int GetExitCodeForAbruptExit(const GlobalVariables& globals);