Build broken for VxWorks on RHEL 7

[jphickey]

Describe the bug
The newest RHEL 7 comes by default with CMake version 2.8.12.2 in the official OS repos.
However the "VERSION_GREATER_EQUAL" comparison was added in 3.7. Thus the build became broken on this platform after merging #610.

To Reproduce
Attempt to build for VxWorks using RHEL 7.x as the host platform. Make file generation fails immediately with:

CMake Error at /home/jphickey/cfecfs/github/osal/src/os/vxworks/CMakeLists.txt:48 (if):
  if given arguments:

    "CMAKE_SYSTEM_VERSION" "VERSION_GREATER_EQUAL" "7.0"

  Unknown arguments specified

Expected behavior
Build should succeed.

Code snips

osal/src/os/vxworks/CMakeLists.txt

Line 48 in d698a4d

if (CMAKE_SYSTEM_VERSION VERSION_GREATER_EQUAL 7.0)

System observed on:
Red Hat Enterprise Linux Workstation release 7.9 (Maipo)

Reporter Info
Joseph Hickey, Vantage Systems, Inc.