MIPS: tweak register constraint to build under clang

lss/linux_syscall_support.h

 /* Copyright (c) 2005-2011, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 2561 matching lines @@
                                  "$11", "$12", "$13", "$14", "$15",           \
                                  "$24", "$25", "hi", "lo", "memory"
     #else
     #define LSS_SYSCALL_CLOBBERS "$1", "$3", "$10", "$11", "$12",             \
                                  "$13", "$14", "$15", "$24", "$25",           \
                                  "hi", "lo", "memory"
     #endif
     #define LSS_BODY(type,name,r7,...)                                        \
           register unsigned long __v0 __asm__("$2") = __NR_##name;            \
           __asm__ __volatile__ ("syscall\n"                                   \
-                                : "+r"(__v0), r7 (__r7)                       \
+                                : "=r"(__v0), r7 (__r7)                       \
                                 : "0"(__v0), ##__VA_ARGS__                    \
                                 : LSS_SYSCALL_CLOBBERS);                      \
           LSS_RETURN(type, __v0, __r7)
     #undef _syscall0
     #define _syscall0(type, name)                                             \
       type LSS_NAME(name)(void) {                                             \
         register unsigned long __r7 __asm__("$7");                            \
         LSS_BODY(type, name, "=r");                                           \
       }
     #undef _syscall1
@@ skipping 1142 matching lines @@
   #endif
   #if defined(__mips__)
     /* sys_pipe() on MIPS has non-standard calling conventions, as it returns
      * both file handles through CPU registers.
      */
     LSS_INLINE int LSS_NAME(pipe)(int *p) {
       register unsigned long __v0 __asm__("$2") = __NR_pipe;
       register unsigned long __v1 __asm__("$3");
       register unsigned long __r7 __asm__("$7");
       __asm__ __volatile__ ("syscall\n"
-                            : "+r"(__v0), "=r"(__v1), "=r" (__r7)
+                            : "=r"(__v0), "=r"(__v1), "=r" (__r7)
                             : "0"(__v0)
                             : "$8", "$9", "$10", "$11", "$12",
                               "$13", "$14", "$15", "$24", "$25", "memory");
       if (__r7) {
         unsigned long __errnovalue = __v0;
         LSS_ERRNO = __errnovalue;
         return -1;
       } else {
         p[0] = __v0;
         p[1] = __v1;
@@ skipping 264 matching lines @@
 # pragma pop_macro("fstat64")
 # pragma pop_macro("lstat64")
 #endif
 
 #if defined(__cplusplus) && !defined(SYS_CPLUSPLUS)
 }
 #endif
 
 #endif
 #endif