build: instruct AGENTS to run static analysis checks (#59137)

Author: vtjnash

AGENTS.md

@@ -27,6 +27,11 @@ If you made changes to the runtime (any files in `src/`), you will need to rebui
 julia. Run `make -j` to rebuild julia. This process may take up to 10 minutes
 depending on your changes.
 
+After `make` run these static analysis checks:
+  - `make -C src clang-sa-<filename>` (replace `<filename>` with the basename of the file you modified)
+  - `make -C src clang-sagc-<filename>` which may require adding JL_GC_PUSH arguments, or JL_GC_PROMISE_ROOTED statements., or require fixing locks. Remember arguments are assumed rooted, so check the callers to make sure that is handled. If the value is being temporarily moved around in a struct or arraylist, `JL_GC_PROMISE_ROOTED(struct->field)` may be needed as a statement (it return void) immediately after reloading the struct before any use of struct. Put the promise as early in the code as is legal.
+  - `make -C src clang-tidy-<filename>`
+
 ## Using Revise
 
 If you have made changes to files included in the system image (base/ or stdlib/),