Install and document FileCheck usage

.github/workflows/auto-sync.yml

@@ -40,8 +40,11 @@ jobs:
         run: |
           sudo apt install llvm-18
           llvm-mc-18 --version
+          FileCheck-18 --version
           sudo ln -s $(whereis -b llvm-mc-18 | grep -Eo "/.*") /usr/local/bin/llvm-mc
+          sudo ln -s $(whereis -b FileCheck-18 | grep -Eo "/.*") /usr/local/bin/FileCheck
           llvm-mc --version
+          FileCheck-18
 
       - name: Clone llvm-capstone
         run: |
@@ -65,6 +68,7 @@ jobs:
         run: |
           sudo apt remove llvm-18
           sudo rm /usr/local/bin/llvm-mc
+          sudo rm /usr/local/bin/FileCheck
 
       - name: Differ - Test save file is up-to-date
         run: |

suite/auto-sync/README.md

@@ -47,13 +47,13 @@ cmake --build . --target llvm-tblgen --config Debug
 cd ../../
 ```
 
-#### Install `llvm-mc`
+#### Install `llvm-mc` and `FileCheck`
 
-Additionally, we need `llvm-mc` for generating our regression tests.
+Additionally, we need `llvm-mc` and `FileCheck` to generate our regression tests.
 You can build it, but it will take a lot of space on your hard drive.
 You can also get the binaries [here](https://releases.llvm.org/download.html) or
 install it with your package manager (usually something like `llvm-18-dev`).
-Just ensure it is in your `PATH` as `llvm-mc`.
+Just ensure it is in your `PATH` as `llvm-mc` and `FileCheck` (not as `llvm-mc-18` or similar though!).
 
 ## Architecture