Puts build-tool args first

build-tool provided args must be considered first by cc, etc. Generally this already occurred for -I flags, because most of our -I flags were -isystem. However it didn't occur for keg-only flags and -L paths.

This was an error.

I amended the refurbishment code to ensure any paths we want to control the order of are thoroughly scrubbed out of the build-tool provided args. This ensures reliability for our builds.

However this path-scrubbing should always occur, even during configure (I am fairly sure of this). So more work is required.

Fixes Homebrew/homebrew#14781.

Library/ENV/4.3/cc

@@ -64,24 +64,24 @@ class Cmd
       refurbished_args
     end
     if tool != 'ld'
-      args.unshift("--sysroot=#$sdkroot")
+      args << "--sysroot=#$sdkroot"
     else
-      args.unshift($sdkroot).unshift("-syslibroot")
+      args << "-syslibroot" << $sdkroot
     end if nclt?
     case mode
     when :cpp
-      %w{-E} + cppflags + args
+      %w{-E} + args + cppflags
     when :ld
       ldflags + args
     when :cc
-      cflags + cppflags + args
+      cflags + args + cppflags
     when :ccld
-      cflags + cppflags + ldflags + args
+      cflags + args + cppflags + ldflags
     end.compact
   end
   def refurbished_args
-    lset = Set.new(syslibpath)
+    lset = Set.new(libpath + syslibpath)
-    iset = Set.new(syscpath)
+    iset = Set.new(cpath.flatten)
 
     args = []
     whittler = @args.each