WIP: Index anonymous structs

[rpigott]

In #2863 I tried to use a fixed name for anonymous structs. That was no good so it was suggested to generate unique names for them. This does basically fix my original use case, but it doesn't seem to have the intended effect. I can still reproduce the crash in some of the test cases though I'm not sure why yet.

Also, some types that I don't think should be anonymous are identified as such:

$ sudo ./src/bpftrace -e 'uprobe:libc:getaddrinfo {printf("%d\n", args.hints->ai_protocol);}'
stdin:1:41-64: ERROR: Struct/union of type 'struct __anon_1' does not contain a field named 'ai_protocol'
uprobe:libc:getaddrinfo {printf("%d\n", args.hints->ai_protocol);}

but hints should have type struct addrinfo * [1].

Intended for #2867

[1] https://debuginfod.archlinux.org/buildid/8bfe03f6bf9b6a6e2591babd0bbc266837d8f658/debuginfo