cmd/internal/obj: clean up brloop
cmd/internal/obj: clean up brloop

Add docs.
Reduce indentation.

Passes toolstash-check -all.

Change-Id: I968d1af25989886ae9945052e05e211a107dde9c
Reviewed-on: https://go-review.googlesource.com/38443
Run-TryBot: Josh Bleecher Snyder <cdc248cc4d32e4fbfe04e45228163bcecd48a0b9@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Cherry Zhang <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>

CAFxX/go,ImJasonH/go,linux-on-ibm-z/go,polyverse-security/go,derekmarcotte/go,linux-on-ibm-z/go,vsekhar/elastic-go,derekmarcotte/go,cloudflare/go,codestation/go,CAFxX/go,nawawi/go,codestation/go,josharian/go,golang/go,CAFxX/go,nawawi/go,linux-on-ibm-z/go,vsekhar/elastic-go,josharian/go,derekmarcotte/go,Cofyc/go,ImJasonH/go,nawawi/go,Cofyc/go,akutz/go,vsekhar/elastic-go,golang/go,codestation/go,cloudflare/go,linux-on-ibm-z/go,linux-on-ibm-z/go,nawawi/go,Cofyc/go,Cofyc/go,codestation/go,polyverse-security/go,codestation/go,josharian/go,CAFxX/go,vsekhar/elastic-go,golang/go,vsekhar/elastic-go,Cofyc/go,cloudflare/go,josharian/go,josharian/go,josharian/go,akutz/go,akutz/go,vsekhar/elastic-go,ImJasonH/go,polyverse-security/go,josharian/go,nawawi/go,CAFxX/go,polyverse-security/go,nawawi/go,cloudflare/go,linux-on-ibm-z/go,CAFxX/go,golang/go,derekmarcotte/go,golang/go,ImJasonH/go,nawawi/go,Cofyc/go,cloudflare/go,ImJasonH/go,linux-on-ibm-z/go,ImJasonH/go,codestation/go,cloudflare/go,polyverse-security/go,akutz/go,polyverse-security/go,linux-on-ibm-z/go,derekmarcotte/go,nawawi/go,akutz/go,Cofyc/go,akutz/go,Cofyc/go,CAFxX/go,vsekhar/elastic-go,golang/go,akutz/go,golang/go,derekmarcotte/go,derekmarcotte/go,polyverse-security/go,golang/go,codestation/go,codestation/go,cloudflare/go,cloudflare/go,akutz/go,josharian/go,christopher-henderson/Go,CAFxX/go,derekmarcotte/go,vsekhar/elastic-go,ImJasonH/go,ImJasonH/go,polyverse-security/go