EMULATE_FUNCTION_POINTER_CASTS + dlsym breaks

Sample code:
```c
// main.c
#include
int main() {
void *handle = dlopen("library.wasm", RTLD_NOW);
typedef void (*fp)();
fp g = (fp) dlsym(handle, "foo");
g();
return 0;
}
```
```c
// library.c
void foo() {}
```
Build script:
```shell
$ emcc library.c -o library.wasm -s SIDE_MODULE=1 -s EXPORT_ALL=1 -s EMULATE_FUNCTION_POINTER_CASTS=1
$ emcc main.c -s MAIN_MODULE=1 -s EXPORT_ALL=1 --embed-file library.wasm -s EMULATE_FUNCTION_POINTER_CASTS=1
$ node a.out.js
```
Error message:
```
exception thrown: RuntimeError: function signature mismatch,RuntimeError: function signature mismatch
at __original_main (:wasm-function[145]:0x6dc93)
at main (:wasm-function[146]:0x6dcae)
at /tmp/dyncall/a.out.js:1506:22
at callMain (/tmp/dyncall/a.out.js:49544:15)
at doRun (/tmp/dyncall/a.out.js:49608:23)
at run (/tmp/dyncall/a.out.js:49623:5)
at runCaller (/tmp/dyncall/a.out.js:49518:19)
at removeRunDependency (/tmp/dyncall/a.out.js:1427:7)
at receiveInstance (/tmp/dyncall/a.out.js:1573:5)
at receiveInstantiatedSource (/tmp/dyncall/a.out.js:1589:5)
```
emcc version: 2.0.10
wasm-opt version: version 91