[sanitizer] Remove rsp from the clobber list in internal_clone

[cryptoad]

Summary

When compiling with WERROR=ON, a new fatal warning started popping up recently
(due to -Werror,-Winline-asm):

.../lib/sanitizer_common/sanitizer_linux.cc:1214:24: error: inline asm clobber list contains reserved registers: RSP [-Werror,-Winline-asm]
                       "syscall\n"
                       ^
<inline asm>:1:1: note: instantiated into assembly here
        syscall
^
.../lib/sanitizer_common/sanitizer_linux.cc:1214:24: note: Reserved registers on the clobber list may not be preserved across the asm statement, and clobbering them may lead to undefined behaviour.
                       "syscall\n"
                       ^
<inline asm>:1:1: note: instantiated into assembly here
        syscall
^

Removing rsp from the clobber list makes the warning go away, and does not
appear to have a functional impact. If there is another way to solve this, let
me know.

[eugenis]

Hmm, I don't see how this assembly clobbers rsp.
If it did, then "return res" after it would not really work.

lib/sanitizer_common/sanitizer_linux.cc

__asm__ __volatile__(
                      "1:\n"
                        : "=a" (res)
                        : "a"(SYSCALL(clone)), "i"(SYSCALL(exit)),
                          "S"(child_stack),
                          "D"(flags),
                          "d"(parent_tidptr),
                          "r"(r8),
                          "r"(r10)
-                       : "rsp", "memory", "r11", "rcx");
+                       : "memory", "r11", "rcx");
   return res;
 }
 #elif defined(__mips__)
 uptr internal_clone(int (*fn)(void *), void *child_stack, int flags, void *arg,
                     int *parent_tidptr, void *newtls, int *child_tidptr) {
   long long res;
   if (!fn || !child_stack)
     return -EINVAL;