Several functions and methods broken when built with `go build -trimpath`

[ChrisHines]

$ go test -trimpath
--- FAIL: TestCallStackString (0.00s)
    stack_test.go:343:
         got []
        want [stack_test.go:362 stack_test.go:335]
--- FAIL: TestCallStackMarshalText (0.00s)
    stack_test.go:357:
         got [91 93]
        want [91 115 116 97 99 107 95 116 101 115 116 46 103 111 58 51 54 50 32 115 116 97 99 107 95 116 101 115 116 46 103 111 58 51 52 56 93]        
--- FAIL: TestTrimRuntime (0.00s)
    stack_test.go:403: got len(trace) == 0, want 1, goroot: "go", trace: []
--- FAIL: TestCallFormat (0.00s)
    stack_test.go:259: fmt.Sprintf("%+s", Call(func)) = github.com/go-stack/stack_test/stack_test.go, want github.com/go-stack/stack/stack_test.go     
    stack_test.go:259: fmt.Sprintf("%+v", Call(func)) = github.com/go-stack/stack_test/stack_test.go:209, want github.com/go-stack/stack/stack_test.go:209
    stack_test.go:259: fmt.Sprintf("%+s", Call(meth)) = github.com/go-stack/stack_test/stack_test.go, want github.com/go-stack/stack/stack_test.go     
    stack_test.go:259: fmt.Sprintf("%+v", Call(meth)) = github.com/go-stack/stack_test/stack_test.go:200, want github.com/go-stack/stack/stack_test.go:200
--- FAIL: Example_callFormat (0.00s)
got:
github.com/go-stack/stack_test/format_test.go
format_test.go:13   Example_callFormat()
want:
github.com/go-stack/stack/format_test.go
format_test.go:13   Example_callFormat()
FAIL
exit status 1
FAIL    github.com/go-stack/stack       0.200s