Conditionally define BPLOG_IF

This allows BPLOG_IF to be overriden by defines in BP_LOGGING_INCLUDE.

Change-Id: Ic6e8373476cc4d1f73d55e13a23686a2c8309fdc
Reviewed-on: https://chromium-review.googlesource.com/c/1278104
Reviewed-by: Ivan Penkov <ivanpe@chromium.org>

src/processor/logging.h

@@ -190,7 +190,9 @@ int ErrnoString(string *error_string);
                         __FILE__, __LINE__)
 #endif  // BPLOG_CRITICAL
 
+#ifndef BPLOG_IF
 #define BPLOG_IF(severity, condition) \
     BPLOG_LAZY_STREAM(severity, ((condition) && BPLOG_LOG_IS_ON(severity)))
+#endif  // BPLOG_IF
 
 #endif  // PROCESSOR_LOGGING_H__