Add Intel ICC 18 detection/support to CMakeLists.txt

[Spudz76]

• Detect ICC-18, add their header and lib paths

• Select newest available and compatible GCC and pass to ICC to avoid built-in default of using /usr/bin/gcc which in some distro revisions is too old

• Use -DICC_GCCVER=N to force specific gcc-N

• Link to Intel lib

[Spudz76]

Fresh on the heels of ICC-19 release, here is ICC-18 support...
I have not yet tried ICC-19

[psychocrypt]

I need to test it by my self. Some changes looks like workarounds for a not correct configured icc.

[psychocrypt]

Please do not hard code any path's. It could be that the compiler is installed somewhere else even if this path is the default path.

[psychocrypt]

Not sure if this is the correct way, because if I install icc I select already an gcc version. This looks like a workaround.

[Spudz76]

What, where? I run the installer, remove everything but the C++, it never asks it only seeks whatever /usr/bin/gcc points to... system default

I also use this to generate test binaries made with every permutation of ICC+GCC regardless what was configured or what the system defaults are. So yes, it is a workaround, for having to use the ICC environment at all (I don't use their shell scripts or whatever). I also don't have ICC in the system path.

[Spudz76]

Example of what happens otherwise:

[ 31%] Building CXX object CMakeFiles/xmr-stak-backend.dir/xmrstak/backend/backendConnector.cpp.o
In file included from /usr/src/xmr-stak/./xmrstak/backend/pool_data.hpp(3),
                 from /usr/src/xmr-stak/./xmrstak/backend/miner_work.hpp(3),
                 from /usr/src/xmr-stak/./xmrstak/backend/globalStates.hpp(3),
                 from /usr/src/xmr-stak/xmrstak/backend/iBackend.hpp(3),
                 from /usr/src/xmr-stak/xmrstak/backend/backendConnector.cpp(24):
/usr/include/c++/8/cstdint(38): catastrophic error: cannot open source file "bits/c++config.h"
  #include <bits/c++config.h>
                             ^

compilation aborted for /usr/src/xmr-stak/xmrstak/backend/backendConnector.cpp (code 4)

It has picked up gcc-8 and crashes out. You probably have never had gcc-8 on the same system as icc-18? This compiler test box has gcc 5,6,7,8 and clang 3.8,3.9,4.0,5.0,6.0,7,8 and icc-18.

icc by itself is too stupid to avoid gcc-8 even though it does not work.

[Spudz76]

Confirmed, I set my system compiler back to gcc-7 and icc works without these mods.
However if /usr/bin/gcc is actually gcc-8 then icc crashes.

I will rework this patch so it is more generic.