Corrected include of C++ header file in AECM that was done using external inclusion

webrtc/modules/audio_processing/aecm/aecm_core.cc

Index: webrtc/modules/audio_processing/aecm/aecm_core.cc
diff --git a/webrtc/modules/audio_processing/aecm/aecm_core.cc b/webrtc/modules/audio_processing/aecm/aecm_core.cc
index 5c3db1a29488d384b6764952c9565c493afe1000..8a5524e04d70ed2264c6ff69a52547da1d485ffc 100644
--- a/webrtc/modules/audio_processing/aecm/aecm_core.cc
+++ b/webrtc/modules/audio_processing/aecm/aecm_core.cc
@@ -17,7 +17,9 @@
 extern "C" {
 #include "webrtc/common_audio/ring_buffer.h"
 #include "webrtc/common_audio/signal_processing/include/real_fft.h"
+}
 #include "webrtc/modules/audio_processing/aecm/echo_control_mobile.h"
+extern "C" {
 #include "webrtc/modules/audio_processing/utility/delay_estimator_wrapper.h"
 #include "webrtc/system_wrappers/include/cpu_features_wrapper.h"
 }