Consistently use e.g.
  if (VARIABLE)
instead of
  if (${VARIABLE})
because the latter causes the variable to be expanded twice (if the
first expansion yields the name of a defined variable).
This is usually not wanted and it also causes the following cmake
snippet

	if (${CMAKE_Fortran_COMPILER_ID} MATCHES "GNU")
		message("This is a GNU compiler")
	else()
		message("This is not a GNU compiler")
	endif()

	set(GNU "foo")

	if (${CMAKE_Fortran_COMPILER_ID} MATCHES "GNU")
		message("This is a GNU compiler")
	else()
		message("This is not a GNU compiler")
	endif()

	if (CMAKE_Fortran_COMPILER_ID MATCHES "GNU")
		message("This is a GNU compiler")
	else()
		message("This is not a GNU compiler")
	endif()

to produce the rather confusing

	This is a GNU compiler
	This is not a GNU compiler
	This is a GNU compiler