Port clock_gettime from GHCJS to the JS backend

GHCJS implemented the c function clock_gettime, which is imported into the time package via the C FFI. Currently, the JavaScript backend has not ported the containing file (rts/js/time.js).

added javascript label

assigned to @JoshMeredith

mentioned in commit 8e52b799

mentioned in merge request !10396 (closed)

added Pnormal Ttask labels

mentioned in commit 9b71f890

mentioned in commit 5e3f9bb5

mentioned in commit 6c5fcaba

Fixed in !10396 (closed)

closed