COMP: Cache VTK_HAS_STD_ISFINITE and related variables.

One week ago (Jul 22) I added code to the CMakeLists.txt to clear
VTK_HAS_STD_ISFINITE, VTK_HAS_STD_ISNAN, and VTK_HAS_STD_ISINF
from the cache, in order to avoid dashboard build errors from
machines that had cached the incorrect values for these variables.
Now that all the dashboards have run, these variable can be persistent
in the cache like most other cache variables.

Change-Id: I38084b25da3328b4f2b833b5654653688b1eb2c5
Merge topic 'clear-std-isfinite' into master

3680d942 COMP: Cache VTK_HAS_STD_ISFINITE and related variables.