cmd/gc: more meaningful names for closures

[dvyukov]

Go users see function names in crash dumps, cpu/memory/goroutine profiles, nm, objdump,
etc.
Names like "net/http.(*persistConn).readLoop" are pretty much representative.
While closure names like "net/http.func·001" are not, you have no idea what
it is and how to identify it.

I propose to add outer function names to closures as:
net/http.(*persistConn).readLoop.func·001
Such names are much more informative that the current ones.

Closures created in global scope stay the same (but now you at least know that it's a
global closure):
net/http.func·001

Closures nested in other closures can be either:
net/http.(*persistConn).readLoop.func·001.func·002
or probably just flattened as:
net/http.(*persistConn).readLoop.func·002

[bradfitz]

Comment 1:

Could the symbol include the code's initial line number?

[rsc]

Comment 2:

Status changed to Duplicate.

Merged into issue #8291.