title: gdb on mac 10.9 fails with "not in executable format: File format not recognized" for 32+64 arch
body: <pre><code>$ file app
  app: Mach-O universal binary with 2 architectures
  app (for architecture i386):    Mach-O executable i386
  app (for architecture x86_64):  Mach-O 64-bit executable x86_64
  
  $ gdb app
  GNU gdb (GDB) 7.6
  Copyright (C) 2013 Free Software Foundation, Inc.
  License GPLv3+: GNU GPL version 3 or later &lt;http://gnu.org/licenses/gpl.html&gt;
  This is free software: you are free to change and redistribute it.
  There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
  and "show warranty" for details.
  This GDB was configured as "x86_64-apple-darwin13.0.0".
  For bug reporting instructions, please see:
  &lt;http://www.gnu.org/software/gdb/bugs/&gt;...
  "app": not in executable format: File format not recognized
  
  
  $ file test
  test: Mach-O 64-bit executable x86_64
  
  $ gdb test
  GNU gdb (GDB) 7.6
  Copyright (C) 2013 Free Software Foundation, Inc.
  License GPLv3+: GNU GPL version 3 or later &lt;http://gnu.org/licenses/gpl.html&gt;
  This is free software: you are free to change and redistribute it.
  There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
  and "show warranty" for details.
  This GDB was configured as "x86_64-apple-darwin13.0.0".
  For bug reporting instructions, please see:
  &lt;http://www.gnu.org/software/gdb/bugs/&gt;...
  Reading symbols from /Users/dmulder/test...Reading symbols from /Users/dmulder/test.dSYM/Contents/Resources/DWARF/test...done.
  done.
  </code></pre>
  
  <p>Why would the 64bit binary succeed, but the 64+32 binary fail?</p>