stacksnoop.lua: undefined symbol bcc_symcache_new

It looks like stacksnoop.lua is broken.

```
# ./stacksnoop.lua ext4_io_submit
[ERROR] bcc.lua:2271: bcc-lua: undefined symbol: bcc_symcache_new
stack traceback:
[C]: in function '__index'
bcc.lua:2271: in function 'SymbolCache'
./stacksnoop.lua:53: in function <./stacksnoop.lua:44>
[C]: in function 'xpcall'
bcc.lua:5913: in function
[C]: at 0x00403ee0
```

I am not sure when it got broken. Can one of lua experts take a look?

Start with stacksnoop.lua around line 53 and bcc.lua around line 2271, where SymbolCache reaches the missing bcc_symcache_new symbol. Reproduce the ./stacksnoop.lua ext4_io_submit command, trace the symbol's definition and linkage, and confirm the command runs without the undefined-symbol error.

Written by the indexing model from the issue text.