Reland of place basictypes.h with stdint.h for int_t types. (patchset #1 id:1 of https://codereview.webrtc.org/2603203003/ )

Reason for revert:
Doing a reland where systeminfo.cc includes basictypes.h so that CPU_X86 etc. are defined when they are checked/used.

Original issue's description:
> Revert of Replace basictypes.h with stdint.h for int_t types. (patchset #1 id:1 of https://codereview.webrtc.org/2604043002/ )
>
> Reason for revert:
> Very likely cause of Chromium import bot breakage (unused function '__cpuid'), TBD why.
>
> Original issue's description:
> > Replace basictypes.h with stdint.h for int_t types.
> >
> > Removes basictypes.h for types that only makes use of it for fixed-size-int
> > typedefs and replaces it with stdint.h.
> >
> > BUG=webrtc:6853
> > R=tommi@webrtc.org
> >
> > Review-Url: https://codereview.webrtc.org/2604043002
> > Cr-Commit-Position: refs/heads/master@{#15867}
> > Committed: https://chromium.googlesource.com/external/webrtc/+/7fd1a753005ca93e8bd934a55808a2137b0ad84f
>
> TBR=tommi@webrtc.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=webrtc:6853
>
> Review-Url: https://codereview.webrtc.org/2603203003
> Cr-Commit-Position: refs/heads/master@{#15869}
> Committed: https://chromium.googlesource.com/external/webrtc/+/7eb0e23bcf675635ef339a519a10563ebc9d93dc

BUG=webrtc:6853
TBR=tommi@webrtc.org

Review-Url: https://codereview.webrtc.org/2609783002
Cr-Commit-Position: refs/heads/master@{#15873}
diff --git a/webrtc/api/rtpreceiver.h b/webrtc/api/rtpreceiver.h
index 4b3bd4d..b6807c4 100644
--- a/webrtc/api/rtpreceiver.h
+++ b/webrtc/api/rtpreceiver.h
@@ -15,13 +15,14 @@
 #ifndef WEBRTC_API_RTPRECEIVER_H_
 #define WEBRTC_API_RTPRECEIVER_H_
 
+#include <stdint.h>
+
 #include <string>
 
 #include "webrtc/api/mediastreaminterface.h"
 #include "webrtc/api/rtpreceiverinterface.h"
 #include "webrtc/api/remoteaudiosource.h"
 #include "webrtc/api/videotracksource.h"
-#include "webrtc/base/basictypes.h"
 #include "webrtc/base/sigslot.h"
 #include "webrtc/media/base/videobroadcaster.h"
 #include "webrtc/pc/channel.h"