This makes type-based queries faster and more robust because they
needn't invoke a C compiler, at the cost of worse results in/near .go
files that import "C". It's particularly important for "referrers"
since a refererrs query on a name from the standard library can load
every package in the workspace.
Fixes issue 10347
Change-Id: I2f65474ce963de5c0897ba67eeb26290dd449cf1
Reviewed-on: https://go-review.googlesource.com/8493
Reviewed-by: David Crawshaw <crawshaw@golang.org>
f0d8175b3e