e.g. ·Name instead of package·Name for automatic stack map to
be applied from its Go prototype.

The underlying reason is that liblink look up name with suffix
".args_stackmap" for the stackmap coming from its Go prototype,
but all the Go functions are named "".Name as this stage. Thus
an assembly function named package·Name will never find its
stackmap, which is named "".package.Name.args_stackmap.

Perhaps cmd/vet should give a warning for this.

Change-Id: I10d154a73ec969d574d20af877f747424350fbd1
Reviewed-on: https://go-review.googlesource.com/2588Reviewed-by: Ian Lance Taylor <iant@golang.org>