Auto merge of #147518 - dianqk:update-llvm, r=cuviper,Kobzol

Update LLVM to 21.1.3

Fixes rust-lang/rust#146742.

After rust-lang/rust#146124, we need more space to run x86_64-gnu-distcheck if building LLVM from source. According to the building log, the space freed by `free-disk-space-linux.sh` is not entirely available.

```
You are running out of disk space.
The runner will stop working when the machine runs out of disk space.
Free space left: 98 MB

disk usage:
Filesystem      Size  Used Avail Use% Mounted on
/dev/root        72G   43G   29G  60% /
tmpfs           7.9G   84K  7.9G   1% /dev/shm
tmpfs           3.2G  1.2M  3.2G   1% /run
tmpfs           5.0M     0  5.0M   0% /run/lock
/dev/sda16      881M   60M  760M   8% /boot
/dev/sda15      105M  6.2M   99M   6% /boot/efi
/dev/sdb1        74G   28K   70G   1% /mnt
tmpfs           1.6G   12K  1.6G   1% /run/user/1001
```

Author: bors