Update toolchain file to fix warnings

[CreepNT]

• Bump minimum version up to silence warnings (and be compatible w/ CMake 4.0)
• Remove CMakeForceCompiler hack using the CMAKE_TRY_COMPILE_TARGET_TYPE option from CMake 3.6+

Resolves the following warnings during build (using CMake 3.25.1):

CMake Deprecation Warning at /usr/local/mepsdk/mep-elf/share/mep-toolchain.cmake:34 (cmake_minimum_required):
  Compatibility with CMake < 2.8.12 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value or use a ...<max> suffix to tell
  CMake that the project does not need compatibility with older versions.
Call Stack (most recent call first):
  build/CMakeFiles/3.25.1/CMakeSystem.cmake:6 (include)
  CMakeLists.txt:11 (project)


CMake Deprecation Warning at /usr/share/cmake-3.25/Modules/CMakeForceCompiler.cmake:75 (message):
  The CMAKE_FORCE_C_COMPILER macro is deprecated.  Instead just set
  CMAKE_C_COMPILER and allow CMake to identify the compiler.
Call Stack (most recent call first):
  /usr/local/mepsdk/mep-elf/share/mep-toolchain.cmake:72 (CMAKE_FORCE_C_COMPILER)
  build/CMakeFiles/3.25.1/CMakeSystem.cmake:6 (include)
  CMakeLists.txt:11 (project)


CMake Deprecation Warning at /usr/share/cmake-3.25/Modules/CMakeForceCompiler.cmake:89 (message):
  The CMAKE_FORCE_CXX_COMPILER macro is deprecated.  Instead just set
  CMAKE_CXX_COMPILER and allow CMake to identify the compiler.
Call Stack (most recent call first):
  /usr/local/mepsdk/mep-elf/share/mep-toolchain.cmake:73 (CMAKE_FORCE_CXX_COMPILER)
  build/CMakeFiles/3.25.1/CMakeSystem.cmake:6 (include)
  CMakeLists.txt:11 (project)