GYP: Add webrtc/pc/pc.gyp:* to 'All' target.

After moving the .isolate targets as part of
https://codereview.webrtc.org/1843193002/
the rtc_pc_unittests_run target was no longer a part
of the 'All' target. This caused it not being built, which
causes Swarming to fail:
https://build.chromium.org/p/client.webrtc.fyi/builders/Linux64%20Release%20%28swarming%29/builds/1678

Adding it to 'All' should fix this.

TBR=pthatcher@webrtc.org
BUG=webrtc:4243

Review URL: https://codereview.webrtc.org/1850143002 .

Cr-Commit-Position: refs/heads/master@{#12195}

webrtc/webrtc.gyp

@@ -15,6 +15,7 @@
       'media/media.gyp:*',
       'modules/modules.gyp:*',
       'p2p/p2p.gyp:*',
+      'pc/pc.gyp:*',
       'system_wrappers/system_wrappers.gyp:*',
       'tools/tools.gyp:*',
       'voice_engine/voice_engine.gyp:*',