[libc] Change fcntl cmd when only fcntl64 is available

In some systems like rv32, only fcntl64 is available and it employs a
different structure for file locking and the correspoding F_GETLK64,
F_SETLK64, and F_SETLKW64 commands.

So if we use fcntl64, the F_GETLK, F_SETLK, and F_SETLKW commands need
to be changed to their 64 versions. This patch adds new cases to the
swich(cmd) in our implementation of fcntl to do that.

The default case was moved to outside the switch, so we don't need to
change anything, the F_GETLK, F_SETLK, and F_SETLKW commands will just
go through the old implementation.

Author: mikhailramalho

libc/src/__support/OSUtil/linux/fcntl.cpp

@@ -86,17 +86,37 @@ int fcntl(int fd, int cmd, void *arg) {
     libc_errno = -ret;
     return -1;
   }
+  case F_GETLK: {
+#if defined(SYS_fcntl64)
+    if constexpr (FCNTL_SYSCALL_ID == SYS_fcntl64)
+      return fcntl(fd, F_GETLK64, arg);
+#endif
+    break;
+  }
+  case F_SETLK: {
+#if defined(SYS_fcntl64)
+    if constexpr (FCNTL_SYSCALL_ID == SYS_fcntl64)
+      return fcntl(fd, F_SETLK64, arg);
+#endif
+    break;
+  }
+  case F_SETLKW: {
+#if defined(SYS_fcntl64)
+    if constexpr (FCNTL_SYSCALL_ID == SYS_fcntl64)
+      return fcntl(fd, F_SETLKW64, arg);
+#endif
+    break;
+  }
   // The general case
-  default: {
-    int retVal = LIBC_NAMESPACE::syscall_impl<int>(
-        FCNTL_SYSCALL_ID, fd, cmd, reinterpret_cast<void *>(arg));
-    if (retVal >= 0) {
-      return retVal;
-    }
-    libc_errno = -retVal;
-    return -1;
+  default:;
   }
+  int retVal = LIBC_NAMESPACE::syscall_impl<int>(FCNTL_SYSCALL_ID, fd, cmd,
+                                                 reinterpret_cast<void *>(arg));
+  if (retVal >= 0) {
+    return retVal;
   }
+  libc_errno = -retVal;
+  return -1;
 }
 
 } // namespace internal