cmd/compile: make tabs narrow in src column of ssa.html
cmd/compile: make tabs narrow in src column of ssa.html

Too deeply nested code is hard to fit in ssa.html.
This CL reduces the tab size to 4 characters.

Change-Id: I08643b0868bce3439567084c7d701654655f23d7
Reviewed-on: https://go-review.googlesource.com/c/142857
Reviewed-by: David Chase <ae171625adc8645b8b79b7e405a6da5aba5341e0@google.com>

cloudflare/go,akutz/go,cloudflare/go,golang/go,nawawi/go,josharian/go,josharian/go,josharian/go,cloudflare/go,golang/go,akutz/go,CAFxX/go,akutz/go,golang/go,nawawi/go,josharian/go,CAFxX/go,josharian/go,nawawi/go,nawawi/go,golang/go,josharian/go,nawawi/go,CAFxX/go,CAFxX/go,nawawi/go,cloudflare/go,golang/go,CAFxX/go,akutz/go,CAFxX/go,akutz/go,akutz/go,CAFxX/go,cloudflare/go,cloudflare/go,akutz/go,josharian/go,josharian/go,cloudflare/go,golang/go,golang/go,cloudflare/go,CAFxX/go,nawawi/go,golang/go,akutz/go,nawawi/go