Fix gn breakage on Fuchsia macOS host builds (#11016)
Fix gn breakage on Fuchsia macOS host builds (#11016)

When building Fuchsia on macOS hosts, ensure that we reference the
correct clang toolchain path. This patch also prevents bitcode
compilation on Fuchsia tree builds on macOS.
aam/engine,jamesr/flutter_engine,cdotstout/sky_engine,jason-simmons/flutter_engine,jason-simmons/sky_engine,Hixie/sky_engine,cdotstout/sky_engine,cdotstout/sky_engine,aam/engine,chinmaygarde/flutter_engine,devoncarew/engine,chinmaygarde/flutter_engine,jamesr/flutter_engine,jamesr/sky_engine,jamesr/sky_engine,jamesr/sky_engine,devoncarew/sky_engine,rmacnak-google/engine,chinmaygarde/sky_engine,aam/engine,tvolkert/engine,mikejurka/engine,devoncarew/sky_engine,mikejurka/engine,devoncarew/sky_engine,devoncarew/sky_engine,flutter/engine,jamesr/flutter_engine,tvolkert/engine,jamesr/flutter_engine,devoncarew/engine,jason-simmons/flutter_engine,tvolkert/engine,rmacnak-google/engine,Hixie/sky_engine,jason-simmons/flutter_engine,devoncarew/sky_engine,jason-simmons/flutter_engine,aam/engine,chinmaygarde/sky_engine,devoncarew/engine,chinmaygarde/flutter_engine,rmacnak-google/engine,aam/engine,jamesr/flutter_engine,chinmaygarde/flutter_engine,devoncarew/engine,devoncarew/engine,Hixie/sky_engine,jason-simmons/sky_engine,tvolkert/engine,jason-simmons/sky_engine,Hixie/sky_engine,aam/engine,chinmaygarde/sky_engine,flutter/engine,mikejurka/engine,jamesr/flutter_engine,aam/engine,jason-simmons/sky_engine,chinmaygarde/flutter_engine,jason-simmons/sky_engine,mikejurka/engine,chinmaygarde/sky_engine,jamesr/sky_engine,Hixie/sky_engine,rmacnak-google/engine,mikejurka/engine,jamesr/flutter_engine,flutter/engine,rmacnak-google/engine,mikejurka/engine,cdotstout/sky_engine,jamesr/sky_engine,mikejurka/engine,flutter/engine,chinmaygarde/sky_engine,cdotstout/sky_engine,Hixie/sky_engine,rmacnak-google/engine,jason-simmons/flutter_engine,jason-simmons/sky_engine,flutter/engine,jason-simmons/flutter_engine,mikejurka/engine,devoncarew/engine,jamesr/sky_engine,mikejurka/engine,chinmaygarde/sky_engine,flutter/engine,tvolkert/engine,chinmaygarde/sky_engine,cdotstout/sky_engine,chinmaygarde/flutter_engine,devoncarew/engine,jason-simmons/flutter_engine,devoncarew/sky_engine,jamesr/flutter_engine,aam/engine,flutter/engine,jason-simmons/sky_engine,cdotstout/sky_engine,tvolkert/engine,Hixie/sky_engine,jamesr/sky_engine,flutter/engine,jason-simmons/flutter_engine,chinmaygarde/flutter_engine,jamesr/flutter_engine,devoncarew/sky_engine,Hixie/sky_engine,tvolkert/engine,rmacnak-google/engine