minor update to build_command_readme

Change-Id: I8071073e6266db1e0777239b5392090ad2170191
Restore TARGET_ARCH_VARIANT_FPU handling

Change-Id: Ifbafddaa1f5d05307a704ee4e570c5b5571fef1d
clean spacing in conditionals

Change-Id: I11ebc9052429f0e5e292a3b43d0cc43af3b364c0