Decoupling rtc_base 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_objc and rtc_base_generic)
and rtc_base will act as a proxy between these targets (this way we can avoid a
circular dependency between rtc_base_generic and rtc_base_objc).

BUG=webrtc:7743

Review-Url: https://codereview.webrtc.org/3001623003
Cr-Original-Commit-Position: refs/heads/master@{#19661}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: a0a5b98937de0f0bf90e17011d2cbc8c632cb409
1 file changed