Update LLVM to 21.1.3

[dianqk]

Fixes #146742.

After #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

[dianqk]

@bors try jobs=x86_64-gnu-distcheck

[rust-bors]

💔 Test for d6659ce failed: CI. Failed jobs:

• try - x86_64-gnu-distcheck (web logs, extended logs)

[dianqk]

@bors try jobs=x86_64-gnu-distcheck

[rustbot]

r? @Mark-Simulacrum

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[rustbot]

⚠️ Warning ⚠️

• Some commits in this PR modify submodules.

  If this was not intentional, see I changed a submodule on accident in the rustc dev guide.

[rust-bors]

☀️ Try build successful (CI)
Build commit: bfdd4ca (bfdd4ca14dcc7a1a42c76b7c45521bde578bc92c, parent: acf243778e6c54cb7d54bee4be88e510e4be123e)