oboe: permit use from C

Test: builds C apps correctly
Change-Id: Icba4537c7e60d527d01fa1d18d9ac549ebf14526
diff --git a/media/liboboe/include/oboe/OboeDefinitions.h b/media/liboboe/include/oboe/OboeDefinitions.h
index b3e2deb..79fef3a 100644
--- a/media/liboboe/include/oboe/OboeDefinitions.h
+++ b/media/liboboe/include/oboe/OboeDefinitions.h
@@ -19,7 +19,11 @@
 
 #include <stdint.h>
 
-typedef int32_t  oboe_handle_t;
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef int32_t  oboe_handle_t; // negative handles are error codes
 typedef int32_t  oboe_result_t;
 typedef int32_t  oboe_sample_rate_t;
 /** This is used for small quantities such as the number of frames in a buffer. */
@@ -174,4 +178,8 @@
     OBOE_SHARING_MODE_COUNT // This should always be last.
 } oboe_sharing_mode_t;
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif // OBOE_OBOEDEFINITIONS_H