Issue with cmake and MKL on laptops

[bena-nasa]

The cmake command may require -DMKL_Fortran=on depending on the MKL, the actually issue seems to be with the FindMKL.cmake in ecbuild.

[mathomp4]

@bena-nasa Did you try changing this bit of esma.cmake:

ESMA_cmake/esma.cmake

Lines 68 to 71 in df6e079

	if (APPLE)
	if (DEFINED ENV{MKLROOT})
	set (MKL_Fortran)
	find_package (MKL REQUIRED)

to be set(MKL_Fortran ON)? It seems equivalent to what's there before.

Or even the full on:

set(MKL_Fortran ON CACHE BOOL "Set MKL_Fortran on")

[tclune]

Hmm. I was lazy and had not even realized that we'd previously added logic outside the FindMKL file. I guess it is not quite correct as it stands.

Probably should instead use

option(MKL_Fortran "Allow building without C bindings for MKL" ON)

@bena-nasa Can you test and submit a PR?