Update CMakeLists.txt fix Linux avr-gcc/g++ error

[classicrocker883]

Description

When using CMakeLists.txt in Linux/Unix, this error pops up:

Click to see error

-- The C compiler identification is unknown
-- The CXX compiler identification is unknown
CMake Error at CMakeLists.txt:127 (project):
  The CMAKE_C_COMPILER:

    avr-gcc

  is not a full path and was not found in the PATH.

  Tell CMake where to find the compiler by setting either the environment
  variable "CC" or the CMake cache entry CMAKE_C_COMPILER to the full path to
  the compiler, or to the compiler name if it is in the PATH.


CMake Error at CMakeLists.txt:127 (project):
  The CMAKE_CXX_COMPILER:

    avr-g++

  is not a full path and was not found in the PATH.

  Tell CMake where to find the compiler by setting either the environment
  variable "CXX" or the CMake cache entry CMAKE_CXX_COMPILER to the full path
  to the compiler, or to the compiler name if it is in the PATH.

I simply use the same copy/paste string(REPLACE), but if there is another easier way like list(APPEND) let me know

Requirements

Benefits

Configurations

Related Issues

Unsure/unable to test Apple or to leave this
if(UNIX) or what.