Allows specifying `LD_FLAGS` during development builds.
```
$ LD_FLAGS="-linkmode=external" make dev
```
Since the version of DTrace on macOS Sierra (On the public beta's at least) has been updated, this allows DTrace to run on Terraform during development/debugging.
```
$ sudo dtrace -n 'pid$target::main.main:entry' -c "terraform apply"
dtrace: description 'pid$target::main.main:entry' matched 1 probe
Apply complete! Resources: 0 added, 0 changed, 0 destroyed.
Outputs:
foo = bar
dtrace: pid 23096 has exited
CPU ID FUNCTION:NAME
2 265673 main.main:entry
```
Also redirects the `@which stringer` command inside the `generate` Makefile target to `/dev/null` so we stop echoing the path to the `stringer` binary on every call to `generate`.
8cbef79dbf