Consider improving the developer experience when using output redirects

[ezzatron]

Say you have a target like this:

foo:
	some-command > foo

Currently, if you run make foo, and some-command fails, foo will be created, and make will exit with a status of 0. Furthermore, a subsequent run of make foo will claim that foo is up-to-date.

We could improve this situation by setting either SHELL or .SHELLFLAGS to enforce Bash's pipefail option. This will cause make to exit with a non-zero status when some-command fails. Unfortunately the foo file will still be created on error, so this doesn't completely solve the issue. We might also want to consider using .DELETE_ON_ERROR, which should in theory handle this last part of the problem.

[jmalloc]

Just some quick and dirty things we could do by convention to at least ensure that the erroneous file doesn't persist:

foo:
	some-command > foo || rm foo

foo:
	output=$$(some-command) && output "$$output" > foo