libtool, binutils: fix darwin linking (#7073)

* libtool: fix linking of libtool on darwin

* binutils, libtool: fix conflicts w/ BSD tools, v2

Fix namespace conflicts with BSD tools in a more elegant fashion,
using a program prefix, similar to Homebrew.

var/spack/repos/builtin/packages/binutils/package.py

@@ -79,4 +79,10 @@ def configure_args(self):
         if '+libiberty' in spec:
             configure_args.append('--enable-install-libiberty')
 
+        # To avoid namespace collisions with Darwin/BSD system tools,
+        # prefix executables with "g", e.g., gar, gnm; see Homebrew
+        # https://github.com/Homebrew/homebrew-core/blob/master/Formula/binutils.rb
+        if spec.satisfies('platform=darwin'):
+            configure_args.append('--program-prefix=g')
+
         return configure_args