Don't set --gcc-toolchain on OSX

Author: staticfloat

src/Runner.jl

@@ -132,9 +132,6 @@ function platform_envs(platform::Platform, host_target="x86_64-linux-gnu")
         # https://github.com/llvm-mirror/clang/blob/f3b7928366f63b51ffc97e74f8afcff497c57e8d/lib/Driver/ToolChains/FreeBSD.cpp
         if occursin("-freebsd", target)
             mapping["LDFLAGS"] *= " -L/opt/$(target)/$(target)/lib"
-        else
-            mapping["CC"] *= " -gcc-toolchain /opt/$(target)"
-            mapping["CXX"] *= " -gcc-toolchain /opt/$(target)"
         end
         # flang isn't a realistic option yet, so we still use gfortran here
         mapping["FC"] = target_tool_path("gfortran")