Simplify loading code from stdin during precompilation. (#43853)

Author: maleadt

base/loading.jl

@@ -1437,7 +1437,7 @@ function create_expr_cache(pkg::PkgId, input::String, output::String, concrete_d
                        --startup-file=no --history-file=no --warn-overwrite=yes
                        --color=$(have_color === nothing ? "auto" : have_color ? "yes" : "no")
                        $trace
-                       --eval 'eval(Meta.parse(read(stdin,String)))'`, stderr = internal_stderr, stdout = internal_stdout),
+                       -`, stderr = internal_stderr, stdout = internal_stdout),
               "w", stdout)
     # write data over stdin to avoid the (unlikely) case of exceeding max command line size
     write(io.in, """