IVGCVSW-5760 Updating BuildGuideCrossCompilation.md
IVGCVSW-5760 Updating BuildGuideCrossCompilation.md

Updated many minor points in the document to correct errors or out of date
references.

Signed-off-by: Colm Donelan <f9860052b68289c6785c07724a8e72ee77c1bf0a@arm.com>
Change-Id: Ie42c186916d9dbff3114a810a97ed25da5a06ca5

ARM-software/armnn,ARM-software/armnn,ARM-software/armnn