Refactored the location of cpp_clean when using CMake

[arango]

Unified the location of cpp_clean in standalone ROMS and ROMS-JEDI for CMake configuration. In Compilers/roms_functions.cmake we now have:

# Functions used in CMake to overcome its rudimentary capabilities.

find_program(
  GREP
  NAMES grep egrep
  DOC "Grep command"
  REQUIRED
)

find_program(
  PERL
  NAMES perl
  DOC "Perl command"
  REQUIRED
)

find_program(
  CPP_CLEAN
  NAMES cpp_clean
  HINTS "${CMAKE_CURRENT_SOURCE_DIR}/ROMS/Bin/"
  DOC "ROMS CPP Clean command"
  REQUIRED
)

find_program(
  CPP_EXECUTABLE
  NAMES cpp
  DOC "C-preprocessor command"
  REQUIRED
)

message( STATUS "CMAKE_SOURCE_DIR=${CMAKE_SOURCE_DIR}" )
message( STATUS "CMAKE_CURRENT_SOURCE_DIR=${CMAKE_CURRENT_SOURCE_DIR}" )
message( STATUS "CPP_CLEAN=${CPP_CLEAN}" )