Hacking on build-aux.git

Misc notes

If you have a dependency on another .mk file includes, include it with include $(dir $(lastword $(MAKEFILE_LIST)))common.mk.
.PHONY targets that you wish to be user-visible should have a ## Help text usage comment. See help.mk for more information.
Wrap your .mk files in
```
 ifeq ($(words $(filter $(abspath $(lastword $(MAKEFILE_LIST))),$(abspath $(MAKEFILE_LIST)))),1)
 …
 endif
```
include guards to make sure they are only included once; similar to how you would with a C header file.
The Make export directive only affects recipes, and does not affect $(shell …). Because of this, you shoud not call go inside of $(shell …), as $GO111MODULE may not have the correct value.
Make sure to pass --fail to curl when downloading things; otherwise it will silently save 404 HTML/XML pages.
Don't depend on anything in ./build-aux/bin/ during clean and clobber rules. The prelude.mk cleanup might remove it before your cleanup bit runs. For Go programs, cd to the program's sourcedirectory, and use go run . to run it:
```
 cd $(dir $(_myfile.mk))bin-go/PROGRAM && GO111MODULE=on go run . ARGS...
```
Only tolerate that grossness in your cleanup rules.

check and check-FOO are .PHONY targets that run tests.
test-FOO is an executable program that when run tests FOO. Perhaps the check-FOO Make target compiles and runs the test-FOO program.
test is the POSIX test(1) command. Don't use it as a Makefile rule name.
(That is, use "check" as a verb, and "test" as a noun.)
Internal "private" variables should be named _snippet-name.VAR; for example, a variable internal to k8s.mk might be named _k8s.push.

Everything should work with GNU Make 3.81 AND newer versions.
- Avoid Make features introduced in 3.82 or later.
- The 3.81→3.82 update changed precedence of pattern rules from "parse-order-based" to "stem-length-based". Be careful that your pattern rules work in BOTH systems.
Requires go 1.11 or newer.
Using -- to separate positional arguments isn't POSIX, but is implemented in getopt(3) and getopt_long(3) in every major libc (including macOS). Therefore, -- working is a reasonable base assumption. Known exceptions:
- macOS chmod
Prefer curl to wget; macOS ships with curl, it doesn't ship with wget.

See "Naming conventions"..
See docs/conventions.md.
Place .PHONY: immediately after the rule definition.
Use pattern rules instead of "old-fashioned suffix rules" (as the GNU Make manual refers to them).