Fixing WebRTC after moving from src/webrtc to src/

In https://webrtc-review.googlesource.com/c/src/+/1560 we moved WebRTC
from src/webrtc to src/ (in order to preserve an healthy git history).
This CL takes care of fixing header guards, #include paths, etc...

NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
TBR=tommi@webrtc.org


Bug: chromium:611808
Change-Id: Iea91618212bee0af16aa3f05071eab8f93706578
Reviewed-on: https://webrtc-review.googlesource.com/1561
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Henrik Kjellander <kjellander@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#19846}
diff --git a/system_wrappers/source/cpu_features_linux.c b/system_wrappers/source/cpu_features_linux.c
index 112ad03..9c56450 100644
--- a/system_wrappers/source/cpu_features_linux.c
+++ b/system_wrappers/source/cpu_features_linux.c
@@ -22,7 +22,7 @@
 #include <errno.h>
 #include <link.h>
 #endif
-#include "webrtc/system_wrappers/include/cpu_features_wrapper.h"
+#include "system_wrappers/include/cpu_features_wrapper.h"
 
 #if defined(WEBRTC_ARCH_ARM_FAMILY)
 #include <asm/hwcap.h>