CMake Warning about Policy CMP0115 (cmake 3.21.4)

[laf0rge]

this happens when building current master with cmake 3.21.4:

CMake Warning (dev) at host/libraries/libbladeRF/CMakeLists.txt:428 (add_library):
  Policy CMP0115 is not set: Source file extensions must be explicit.  Run
  "cmake --help-policy CMP0115" for policy details.  Use the cmake_policy
  command to set the policy and suppress this warning.

  File:

    /space/home/laforge/projects/git/bladeRF/host/libraries/libbladeRF/src/version.h.in
This warning is for project developers.  Use -Wno-dev to suppress it.

as the message states it is not critical, but it seems like something that needs cleanup.