Patch 1 from Frederic Picca: detect 64bit and x86 separately

cmake/BornAgain/Linux.cmake

 set(BORNAGAIN_ARCHITECTURE linux)
 set(BORNAGAIN_PLATFORM linux)
 
-execute_process(COMMAND uname -m OUTPUT_VARIABLE SYSCTL_OUTPUT)
-if(${SYSCTL_OUTPUT} MATCHES x86_64)
+if(CMAKE_SIZEOF_VOID_P GREATER 4)
     message(STATUS "Found a 64bit system")
-    set(BIT_ENVIRONMENT "-m64")
-    set(BORNAGAIN_ARCHITECTURE linuxx8664)
+    if(${CMAKE_SYSTEM_PROCESSOR} STREQUAL x86_64)
+        set(BORNAGAIN_ARCHITECTURE linuxx8664)
+    endif()
 else()
     message(STATUS "Found a 32bit system")
-    set(BIT_ENVIRONMENT "-m32")
     add_definitions(-DEIGEN_DONT_ALIGN_STATICALLY=1)
 endif()