ANDROID: Allow MODVERSIONS + Rust with no symbol export

We have two patches [1] [2] which provide proper MODVERSIONS support,
with no current objections. Since they're not in yet though, this is the
lowest impact way to allow the new `ashmem` driver to be tested, as it
does not need module support. Once these are merged upstream, we can
back this out.

[1] https://lore.kernel.org/all/20240925233854.90072-1-mmaurer@google.com/
[2] https://lore.kernel.org/all/20241008183823.36676-21-samitolvanen@google.com/

Bug: 347787665
Change-Id: I979def75f67d1e140253795c0fc706133d23e506
Signed-off-by: Matthew Maurer <mmaurer@google.com>

init/Kconfig

@@ -1942,7 +1942,6 @@ config RUST
 	bool "Rust support"
 	depends on HAVE_RUST
 	depends on RUST_IS_AVAILABLE
-	depends on !MODVERSIONS
 	depends on !GCC_PLUGIN_RANDSTRUCT
 	depends on !RANDSTRUCT
 	depends on !DEBUG_INFO_BTF || PAHOLE_HAS_LANG_EXCLUDE

rust/exports.c

@@ -13,7 +13,7 @@
 
 #include <linux/export.h>
 
-#define EXPORT_SYMBOL_RUST_GPL(sym) extern int sym; EXPORT_SYMBOL_GPL(sym)
+#define EXPORT_SYMBOL_RUST_GPL(sym) extern int sym;
 
 #include "exports_core_generated.h"
 #include "exports_alloc_generated.h"