LHCbMath - Fix undefined behaviour sanitizer warnings from Lomont.cpp
fixes warnings like
workspace/build/LHCB/LHCB_HEAD/Kernel/LHCbMath/src/Lomont.cpp:194:31: runtime error: signed integer overflow: -9223372036854775808 - 4607227454796291113 cannot be represented in type 'long int'
I also skip the Lomont CPU test when running a sanitizer build, as CPU times are skewed so test is meaningless.