Add nacl-clang testing to SCons

tests/gdb/gdb_test_guest.c

 /*
  * Copyright (c) 2012 The Native Client Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include <alloca.h>
 #include <assert.h>
 #include <fcntl.h>
 #include <stdint.h>
@@ skipping 88 matching lines @@
   int local_var = 2 * arg;
   global_var += local_var + arg;
 }
 
 void mmap_breakpoint(void) {
   global_var = 0;
 }
 
 void ret_sequence(void) {
 #if defined(__i386__)
-  asm(
+  __asm__(
       ".globl ret_start\n"
       ".globl ret_end\n"
       ".align 32\n"
       "ret_start:\n"
       "naclret\n"
       "ret_end:\n");
 #elif defined(__x86_64__)
-  asm(
+  __asm__(
       ".globl ret_start\n"
       ".globl ret_end\n"
       ".align 32\n"
       "ret_start:\n"
       "naclret\n"
       "ret_end:\n");
 #endif
 }
 
 typedef void (*func_t)(void);
@@ skipping 164 matching lines @@
   }
   if (strcmp(test_command, "invalid_memory") == 0) {
     return 0;
   }
   if (strcmp(test_command, "mmap") == 0) {
     test_mmap();
     return 0;
   }
   return 1;
 }