Fix #ifdef

GHC is now compiled with -Werror=undef; explicitly use #ifdef instead
of #if

test using "#ifdef" for HAVE_CLOCK_GETTIME

Gabor Greif authored 8 years ago and Ben Gamari committed 8 years ago

GHC has recently tightened preprocessor checks,
so this "#elif" started to fail.

Merge orphan commit into branch 'upstream/master'

Sometime in mid-January there was a force-push to upstream's `master`
repository, making 6e202edc an orphan
commit. Unfortunately, there was a period of time when GHC's `time`
submodule referred to this commit, which means that we need to ensure it
remains accessible in the history. This merge folds this commit into the
`master` branch.