[kfr] build failure

**Host Environment**
- OS: Linux x64
- Compiler: GCC 7.5
- Cmake: 3.19.2

**To Reproduce**
Steps to reproduce the behavior:
`./vcpkg install kfr:x64-linux`

**Failure logs**
Computing installation plan...
The following packages will be built and installed:
kfr[core]:x64-linux -> 2020-06-15
Detecting compiler hash for triplet x64-linux...
Could not locate cached archive: /home/ubuntu/.cache/vcpkg/archives/1b/1b03ddb697fe7ad42e54e72bcf775dca20263d47.zip
Starting package 1/1: kfr:x64-linux
Building package kfr[core]:x64-linux...
CMake Error at scripts/cmake/vcpkg_fail_port_install.cmake:97 (message):
Target 'Linux' not supported by kfr!

Call Stack (most recent call first):
ports/kfr/portfile.cmake:1 (vcpkg_fail_port_install)
scripts/ports.cmake:128 (include)

Error: Building package kfr:x64-linux failed with: BUILD_FAILED
Please ensure you're using the latest portfiles with `./vcpkg update`, then
submit an issue at https://github.com/Microsoft/vcpkg/issues including:
Package: kfr:x64-linux
Vcpkg version: 2021-01-13-unknownhash