[libc] use correct syscall define for SYS__llseek

[gytsen]

Summary

Prior to this revision, the preprocessor would correctly look for the
definition of SYS__llseek. However, the resulting call to syscall(2)
would be done in this branch using SYS__lseek.

Fix this by calling syscall(2) using SYS__llseek.

fixes #56122

[gytsen]

I don't seem to have permissions to be able to merge this. Would someone with write access be able to merge this?

[sivachandra]

Just following up - this was fixed by https://reviews.llvm.org/D133022

libc/src/__support/File/linux_file.cpp

 }
 
 int seek_func(File *f, long offset, int whence) {
   auto *lf = reinterpret_cast<LinuxFile *>(f);
 #ifdef SYS_lseek
   long ret = __llvm_libc::syscall(SYS_lseek, lf->get_fd(), offset, whence);
 #elif defined(SYS__llseek)
   long result;
-  long ret = __llvm_libc::syscall(SYS__lseek, lf->get_fd(), offset >> 32,
+  long ret = __llvm_libc::syscall(SYS__llseek, lf->get_fd(), offset >> 32,
                                   offset, &result, whence);
 #else
 #error "lseek and _llseek syscalls not available to perform a seek operation."
 #endif
 
   if (ret < 0) {
     errno = -ret;
     return -1;