[OpenBSD] -buildmode=pie not supported on openbsd/amd64

[B-Interactive]

Describe the bug

When building maddy via build.sh, it fails with the error -buildmode=pie not supported on openbsd/amd64:

Steps to reproduce

build.sh (at the time of writing this) has existing issues on BSD systems, related to the version of getopt native to those systems, that doesn't support the necessary GNU extensions. As such, gnugetopt must be installed and referenced in order to get this far. Details below.

1. Install go from packages.
2. Install bash from packages.
3. Install gnugetopt from packages.
4. Modify build.sh so line 3 references gnugetopt instead of getopt.

options=$(gnugetopt -o hb:p:d: -l help,builddir:,prefix:,destdir:,systemddir:,configdir:,statedir:,runtimedir:,fail2bandir:,tags:,prefix:,gitversion:,version:,source:,sudo -- "$@")

5. Run ./build.sh:

# bash ./build.sh

6. Build fails with error:

bash-5.0# ./build.sh
                                _|        _|
_|_|_|  _|_|      _|_|_|    _|_|_|    _|_|_|  _|    _|
_|    _|    _|  _|    _|  _|    _|  _|    _|  _|    _|
_|    _|    _|  _|    _|  _|    _|  _|    _|  _|    _|
_|    _|    _|    _|_|_|    _|_|_|    _|_|_|    _|_|_|
                                                    _|
 All-in-one composable mail server.             _|_|

--- Using system Go toolchain (1.15.2, /usr/local/bin/go).
--- WARNING: Source tree is not a Git repository and no version specified.
--- Downloading dependencies...
go: downloading github.com/foxcpp/go-mockdns v0.0.0-20200531120619-ae750bbf9d73
--- Building main executable...
-buildmode=pie not supported on openbsd/amd64

Environment information

• OpenBSD version: 6.8 amd64
• maddy version: 0.4.2
• go version: 1.15.2
• gnugetopt version: 1.1.6p2
• bash version: 5.0.18

Notes

There was apparently a patch for Go that would appear to have enabled buildmode=pie on OpenBSD, for Go 1.11. Seems strange it's cropping up here given that.
cmd/go: static linking fails on OpenBSD 6.2

[foxcpp]

New build.sh script does not unconditionally use -buildmode=pie so this issue can be considered resolved.