Preserve even more of the broken Genrule symlink behavior
Preserve even more of the broken Genrule symlink behavior

Summary:
Turns out the Genrule symlink behavior could also have duplicate
entries for a given key. One could hit this by depending on two cxx rules
that build with different platforms.

Test Plan: CI

Reviewed By: beefon

fbshipit-source-id: 7a00faa

shybovycha/buck,facebook/buck,ilya-klyuchnikov/buck,facebook/buck,robbertvanginkel/buck,k21/buck,Addepar/buck,Addepar/buck,zpao/buck,marcinkwiatkowski/buck,JoelMarcey/buck,JoelMarcey/buck,dsyang/buck,ilya-klyuchnikov/buck,robbertvanginkel/buck,dsyang/buck,romanoid/buck,shybovycha/buck,zhan-xiong/buck,clonetwin26/buck,k21/buck,shs96c/buck,SeleniumHQ/buck,JoelMarcey/buck,Addepar/buck,kageiit/buck,robbertvanginkel/buck,SeleniumHQ/buck,shybovycha/buck,rmaz/buck,Addepar/buck,robbertvanginkel/buck,marcinkwiatkowski/buck,romanoid/buck,dsyang/buck,zhan-xiong/buck,nguyentruongtho/buck,clonetwin26/buck,ilya-klyuchnikov/buck,clonetwin26/buck,rmaz/buck,brettwooldridge/buck,facebook/buck,ilya-klyuchnikov/buck,rmaz/buck,dsyang/buck,dsyang/buck,nguyentruongtho/buck,clonetwin26/buck,SeleniumHQ/buck,LegNeato/buck,JoelMarcey/buck,shs96c/buck,robbertvanginkel/buck,marcinkwiatkowski/buck,shybovycha/buck,robbertvanginkel/buck,clonetwin26/buck,shs96c/buck,LegNeato/buck,zpao/buck,rmaz/buck,zhan-xiong/buck,zhan-xiong/buck,shs96c/buck,ilya-klyuchnikov/buck,zhan-xiong/buck,shybovycha/buck,ilya-klyuchnikov/buck,Addepar/buck,shybovycha/buck,JoelMarcey/buck,k21/buck,facebook/buck,rmaz/buck,rmaz/buck,robbertvanginkel/buck,k21/buck,LegNeato/buck,SeleniumHQ/buck,shybovycha/buck,shs96c/buck,shs96c/buck,romanoid/buck,dsyang/buck,facebook/buck,shybovycha/buck,zhan-xiong/buck,rmaz/buck,k21/buck,ilya-klyuchnikov/buck,JoelMarcey/buck,shybovycha/buck,nguyentruongtho/buck,kageiit/buck,clonetwin26/buck,ilya-klyuchnikov/buck,clonetwin26/buck,SeleniumHQ/buck,rmaz/buck,dsyang/buck,zhan-xiong/buck,JoelMarcey/buck,JoelMarcey/buck,SeleniumHQ/buck,clonetwin26/buck,marcinkwiatkowski/buck,zhan-xiong/buck,SeleniumHQ/buck,Addepar/buck,shs96c/buck,romanoid/buck,SeleniumHQ/buck,LegNeato/buck,kageiit/buck,rmaz/buck,zpao/buck,Addepar/buck,nguyentruongtho/buck,brettwooldridge/buck,LegNeato/buck,romanoid/buck,k21/buck,k21/buck,zhan-xiong/buck,rmaz/buck,brettwooldridge/buck,rmaz/buck,SeleniumHQ/buck,romanoid/buck,romanoid/buck,dsyang/buck,robbertvanginkel/buck,shybovycha/buck,LegNeato/buck,kageiit/buck,zpao/buck,romanoid/buck,ilya-klyuchnikov/buck,robbertvanginkel/buck,marcinkwiatkowski/buck,ilya-klyuchnikov/buck,LegNeato/buck,k21/buck,Addepar/buck,zpao/buck,marcinkwiatkowski/buck,clonetwin26/buck,shs96c/buck,facebook/buck,brettwooldridge/buck,brettwooldridge/buck,marcinkwiatkowski/buck,shs96c/buck,marcinkwiatkowski/buck,Addepar/buck,zhan-xiong/buck,JoelMarcey/buck,k21/buck,marcinkwiatkowski/buck,zpao/buck,nguyentruongtho/buck,zpao/buck,robbertvanginkel/buck,shs96c/buck,romanoid/buck,robbertvanginkel/buck,clonetwin26/buck,dsyang/buck,kageiit/buck,brettwooldridge/buck,dsyang/buck,robbertvanginkel/buck,robbertvanginkel/buck,brettwooldridge/buck,romanoid/buck,kageiit/buck,clonetwin26/buck,zhan-xiong/buck,LegNeato/buck,dsyang/buck,brettwooldridge/buck,zhan-xiong/buck,brettwooldridge/buck,Addepar/buck,nguyentruongtho/buck,dsyang/buck,shs96c/buck,SeleniumHQ/buck,shybovycha/buck,k21/buck,Addepar/buck,k21/buck,kageiit/buck,LegNeato/buck,rmaz/buck,marcinkwiatkowski/buck,romanoid/buck,JoelMarcey/buck,marcinkwiatkowski/buck,LegNeato/buck,SeleniumHQ/buck,brettwooldridge/buck,SeleniumHQ/buck,Addepar/buck,brettwooldridge/buck,JoelMarcey/buck,SeleniumHQ/buck,LegNeato/buck,JoelMarcey/buck,ilya-klyuchnikov/buck,LegNeato/buck,facebook/buck,marcinkwiatkowski/buck,JoelMarcey/buck,romanoid/buck,shybovycha/buck,marcinkwiatkowski/buck,nguyentruongtho/buck,shs96c/buck,romanoid/buck,zhan-xiong/buck,clonetwin26/buck,k21/buck,ilya-klyuchnikov/buck,brettwooldridge/buck,rmaz/buck,LegNeato/buck,ilya-klyuchnikov/buck,Addepar/buck,dsyang/buck,shybovycha/buck,brettwooldridge/buck,clonetwin26/buck,k21/buck,shs96c/buck