rust/arm 32-bit: remove guard for rust-bindgen bug

On 32-bit arm, `size_t` and 'uintptr_t` are incompatible,
which will trigger the static assertion.

The bug which this guard protects against
(rust-lang/rust-bindgen#1671)
was fixed upstream as of rust-bindgen v0.53:
rust-lang/rust-bindgen#1688
d650823839f7 ("Remove size_t to usize conversion")

The current recommended rust-bindgen version for building
the Linux kernel is v0.56, so the guard can be safely
dropped.

Out of an abundance of caution, remove the guard only
if building for 32-bit arm.

Signed-off-by: Sven Van Asbroeck <thesven73@gmail.com>

rust/helpers.c

@@ -81,6 +81,8 @@ void rust_helper_kunmap(struct page *page)
 }
 EXPORT_SYMBOL_GPL(rust_helper_kunmap);
 
+#if !defined(CONFIG_ARM)
 // See https://github.com/rust-lang/rust-bindgen/issues/1671
 static_assert(__builtin_types_compatible_p(size_t, uintptr_t),
 	"size_t must match uintptr_t, what architecture is this??");
+#endif