runtime: look up funcInfo by func pointer
runtime: look up funcInfo by func pointer

runtime.Func.{Name,FileLine} need to be able to
go from a *_func to a funcInfo. The missing bit of
information is what module contains that *_func.

The existing implementation looked up the module
using the *_func's entry PC. A subsequent change will
store *_func's entry PC relative to the containing module.
Change the module lookup to instead for the module
whose pclntable contains the *_func,
cutting all dependencies on the contents of the *_func.

Change-Id: I2dbbfec043ebc2e9a6ef19bbdec623ac84353b10
Reviewed-on: https://go-review.googlesource.com/c/go/+/351458
Trust: Josh Bleecher Snyder <cdc248cc4d32e4fbfe04e45228163bcecd48a0b9@gmail.com>
Run-TryBot: Josh Bleecher Snyder <cdc248cc4d32e4fbfe04e45228163bcecd48a0b9@gmail.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Cherry Mui <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>

golang/go,golang/go,cloudflare/go,golang/go,golang/go,CAFxX/go,nawawi/go,CAFxX/go,golang/go,golang/go,cloudflare/go,cloudflare/go,CAFxX/go,CAFxX/go,CAFxX/go,nawawi/go,nawawi/go,cloudflare/go,golang/go,nawawi/go,golang/go,CAFxX/go,cloudflare/go,CAFxX/go,nawawi/go,nawawi/go,cloudflare/go,nawawi/go,cloudflare/go,cloudflare/go,CAFxX/go,nawawi/go