detect undefined global symbols at load-time
workaround bug in ld regarding nested arithmetic

for whatever reason, if I try to do p2v offset on a single line, the resulting value is off-by-0x10000
some comments to help do really early serial port output if needed
some linking changes to support new gcc

definition for 'raise', use of libgcc to supply aeabi_uidiv function, and finagling of linker flags for this