Limit linear memories when fuzzing with pooling (#4918)

This commit limits the maximum number of linear memories when the
pooling allocator is used to ensure that the virtual memory mapping for
the pooling allocator itself can succeed. Currently there are a number
of crashes in the differential fuzzer where the pooling allocator can't
allocate its mapping because the maximum specified number of linear
memories times the number of instances exceeds the address space
presumably.

crates/fuzzing/src/generators/config.rs

@@ -349,6 +349,11 @@ impl<'a> Arbitrary<'a> for Config {
                 }
             };
 
+            // Don't allow too many linear memories per instance since massive
+            // virtual mappings can fail to get allocated.
+            cfg.min_memories = cfg.min_memories.min(10);
+            cfg.max_memories = cfg.max_memories.min(10);
+
             // Force this pooling allocator to always be able to accommodate the
             // module that may be generated.
             limits.memories = cfg.max_memories as u32;