Bug 1010028 - Set args properly for various debuggers. r=glandium

Set args properly to to separate the debugger and process arguments.
Also add "--args" automatically for gdb front-end cgdb and ddd.

Verification Steps:
1. mach debug +debugger gdb
2. Make sure gdb is launched correctly.

python/mozbuild/mozbuild/mach_commands.py

@@ -767,8 +767,6 @@ class DebugProgram(MachCommandBase):
         help='Do not set the JS_DISABLE_SLOW_SCRIPT_SIGNALS env variable; when not set, recoverable but misleading SIGSEGV instances may occur in Ion/Odin JIT code')
     def debug(self, params, remote, background, debugger, debugparams, slowscript):
         import which
-        use_lldb = False
-        use_gdb = False
         if debugger:
             try:
                 debugger = which.which(debugger)
@@ -779,11 +777,9 @@ class DebugProgram(MachCommandBase):
         else:
             try:
                 debugger = which.which('gdb')
-                use_gdb = True
             except Exception:
                 try:
                     debugger = which.which('lldb')
-                    use_lldb = True
                 except Exception as e:
                     print("You don't have gdb or lldb in your PATH")
                     print(e)
@@ -809,10 +805,17 @@ class DebugProgram(MachCommandBase):
             print(e)
             return 1
 
-        if use_gdb:
-            args.append('--args')
-        elif use_lldb:
-            args.append('--')
+        # args added to separate the debugger and process arguments.
+        args_separator = {
+            'gdb': '--args',
+            'ddd': '--args',
+            'cgdb': '--args',
+            'lldb': '--'
+        }
+
+        debugger_name = os.path.basename(debugger)
+        if debugger_name in args_separator:
+            args.append(args_separator[debugger_name])
         args.append(binpath)
 
         if not remote: