Fix Mac-specific issues

[valassi]

As a part of PR #367 about shared libraries, I added rpath to the executable builds, to make it unnecessary to add LD_LIBRARY_PATH (or DYLD_LIBRARY_PATH). The rpath ORIGIN does not work on Mac,

c++ -o check.exe ./check_sa.o  -ldl -pthread -L../../lib -lmg5amc_common -Wl,-rpath='$ORIGIN/../../lib'   -L../../lib -lmg5amc_cxx
ld: unknown option: -rpath=$ORIGIN/../../lib
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [check.exe] Error 1

I will need to fix that.
https://github.com/madgraph5/madgraph4gpu/runs/5074122375?check_suite_focus=true
https://stackoverflow.com/questions/26280738

En passant I noticed that there are also a few other issues, eg /proc/cpuinfo does not exist on Mac.

I open thic catch-all issues to fix all of these in the various makefiles and scripts (and possibly in code if necessary?)

[valassi]

I attempted a patch but this also fails
https://github.com/madgraph5/madgraph4gpu/runs/5077494059?check_suite_focus=true

c++ -o check.exe ./check_sa.o  -ldl -pthread -L../../lib -lmg5amc_common -Wl,-rpath='@executable_path/../../lib'   -L../../lib -lmg5amc_cxx
ld: unknown option: -rpath=@executable_path/../../lib
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [check.exe] Error 1

[valassi]

Replacing "-rpath=" by "-rpath," makes the build succeed but the runtime fails
https://github.com/madgraph5/madgraph4gpu/runs/5077528086?check_suite_focus=true

c++ -o runTest.exe ./CPPProcess.o ./RandomNumberKernels.o ./RamboSamplingKernels.o ./MatrixElementKernels.o ./BridgeKernels.o ./CrossSectionKernels.o ./testxxx.o  ./testmisc.o  ./runTest.o -ldl -pthread -L../../lib -lmg5amc_common -L../../../../../test/googletest/build/lib/ -lgtest -lgtest_main -Wl,-rpath,'@executable_path/../../lib' 
...
./runTest.exe
dyld: Library not loaded: ../lib/libmg5amc_common.so
  Referenced from: /Users/runner/work/madgraph4gpu/madgraph4gpu/epochX/cudacpp/ee_mumu/SubProcesses/P1_Sigma_sm_epem_mupmum/./runTest.exe
  Reason: image not found
make: *** [runTest] Abort trap: 6

To be debugged

[valassi]

I have added a temporary patch, adding back LD_LIBRARY_PATH to the runtime in 'make check', This makes the CI succeed at least. I will add a better patch when I can debug it.
1222ac1

[valassi]

I have temporarely disabled the build of the Fortran executables on Mac in the CI #376

[valassi]

I have reenabled the Mac build of Fortran executables thanks to Stephan's fixes in #377 and #378

[valassi]

Next issue!
https://github.com/madgraph5/madgraph4gpu/runs/5095459792?check_suite_focus=true#step:4:72

c++  -O3  -std=c++17 -I. -I../../src -I../../../../../tools  -Wall -Wshadow -Wextra -ffast-math    -DMGONGPU_FPTYPE_DOUBLE -DMGONGPU_HAS_NO_CURAND  -fPIC -c fsampler.cc -o fsampler.o
c++ -o fcheck.exe ./fcheck_sa.o ./fsampler.o -L../../lib -lmg5amc_common -Wl,-rpath,'@executable_path/../../lib'   -lgfortran -L../../lib -lmg5amc_cxx
ld: library not found for -lgfortran
clang: error: linker command failed with exit code 1 (use -v to see invocation)

[valassi]

Fixed the -lgfortran issue by this hack

ifeq ($(UNAME_S),Darwin)
$(fcxx_main): LIBFLAGS += -L$(shell dirname $(shell $(FC) --print-file-name libgfortran.dylib)) # add path to libgfortran on Mac #375
endif