[FIX] Corrected bitness check for 64-bit systems

[AhmedYasserrr]

[FIX] Corrected bitness check and added help option to build script

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Description of Changes

Fixed an issue in the bitness check in linux/build.sh:

   if [ "$bit_os"=="64" ]

Fixed missing spaces around == in bitness check. Without the spaces, the condition always evaluated to true, causing -DGPAC_64_BITS to be added even on non-64-bit systems.