cmd/internal/pkgpath: use MustHaveExec in TestToSymbolFunc
cmd/internal/pkgpath: use MustHaveExec in TestToSymbolFunc

ToSymbolFunc executes a command using exec.Command.

Change-Id: Ic6c274bdc23050d021ec98ba67748338ac34f12c
Reviewed-on: https://go-review.googlesource.com/c/go/+/435236
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Auto-Submit: Tobias Klauser <0a68dd4915066ec5d3f81f75a828fee53dcc8822@gmail.com>
Reviewed-by: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@google.com>
Run-TryBot: Tobias Klauser <0a68dd4915066ec5d3f81f75a828fee53dcc8822@gmail.com>

golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go