Decoupling rtc_base_approved from Obj-C code

The goal of this CL is to separate Obj-C/Obj-C++ code from targets which have
also C++ code (see https://bugs.chromium.org/p/webrtc/issues/detail?id=7743
for more information).

To achieve this we have created 2 targets (rtc_base_approved_objc and
rtc_base_approved_generic) and rtc_base_approved will act as a proxy between
these targets (this way we can avoid a circular dependency between
rtc_base_approved_generic and rtc_base_approved_objc).

BUG=webrtc:7743
NOTRY=True

Review-Url: https://codereview.webrtc.org/2988433002
Cr-Original-Commit-Position: refs/heads/master@{#19767}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: bc378479787930b511b151b278318516492bc9fc
1 file changed