bool is used in this header and so stdbool.h is necessary. Add to
avoid compilation errors that aren't currently seen due to transitive
dependencies.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/expr.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/perf/util/expr.h b/tools/perf/util/expr.h
index c0cec29ddc29..d4166b3eb654 100644
--- a/tools/perf/util/expr.h
+++ b/tools/perf/util/expr.h
@@ -2,6 +2,8 @@
 #ifndef PARSE_CTX_H
 #define PARSE_CTX_H 1
 
+#include <stdbool.h>
+
 struct hashmap;
 struct metric_ref;
 
-- 
2.44.0.278.ge034bb2e1d-goog