test: add repro for ocaml#9538 (subst on 32-bit) (ocaml#9539)

Signed-off-by: Etienne Millon <[email protected]>

test/blackbox-tests/test-cases/subst/32bit.t

@@ -0,0 +1,35 @@
+When dune subst is called on a file larger than 16MiB, it should not crash.
+See #9538.
+
+  $ cat > create.ml << EOF
+  > let () = Unix.truncate "large.dat" 0x1_00_00_00
+  > EOF
+  $ touch large.dat
+  $ ocaml unix.cma create.ml
+  $ rm create.ml
+
+  $ cat > dune-project << EOF
+  > (lang dune 1.0)
+  > (name project)
+  > (package
+  >  (name project))
+  > EOF
+
+This test uses subst, which needs a git repository:
+
+  $ git init
+  Initialized empty Git repository in $TESTCASE_ROOT/.git/
+  $ git add dune-project
+  $ git add large.dat
+  $ git commit -m create | tail -n 3
+   2 files changed, 4 insertions(+)
+   create mode 100644 dune-project
+   create mode 100644 large.dat
+
+  $ dune subst 2>&1 | head -n 6
+  Error: exception Invalid_argument("Bytes.create")
+  Raised by primitive operation at Stdune__Io.Make.eagerly_input_string in file
+    "otherlibs/stdune/src/io.ml", line 273, characters 14-30
+  Called from Stdune__Io.Make.read_all.(fun) in file
+    "otherlibs/stdune/src/io.ml", line 308, characters 16-40
+  Called from Stdune__Exn.protectx in file "otherlibs/stdune/src/exn.ml", line

test/blackbox-tests/test-cases/subst/dune

@@ -0,0 +1,5 @@
+(cram
+ (applies_to 32bit)
+ (enabled_if
+  (not %{arch_sixtyfour}))
+ (deps %{bin:git}))