Previously the +build line was taken as a package comment, due to how Go
handles cases like the following:
// +build <foo>
package foo
And thus caused build failures because of package name conflict issues.
Fixes: https://golang.org/cl/152677
Change-Id: I7360ee100a739b00beaa1337b0408bb06fa240a6
GitHub-Last-Rev: b67a58691f3a5be12f2c5c510fbb4bd95fdd6e05
GitHub-Pull-Request: golang/sys#28
Reviewed-on: https://go-review.googlesource.com/c/155748
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
