enable 32/64 bit cross compilation

Signed-off-by: Ferry Huberts <f.huberts@mindef.nl>
fix typoo in previous commit

Signed-off-by: Ferry Huberts <f.huberts@mindef.nl>
make: ifdef fixup

Signed-off-by: Ferry Huberts <f.huberts@mindef.nl>
make: add 32/64 bit cross compilation flag detection

Signed-off-by: Ferry Huberts <f.huberts@mindef.nl>
make: setup correct 32/64 cross compilation compiler/linker flags

Signed-off-by: Ferry Huberts <f.huberts@mindef.nl>
parse: fix parsing of date in GPRMC

It appears that the field is optional/can be empty and that parsing
such an empty field would fail.

Signed-off-by: Ferry Huberts <f.huberts@mindef.nl>
parse: fixup the previous commit

Signed-off-by: Ferry Huberts <f.huberts@mindef.nl>
fix #3/github#5: _nmea_parse_time not parsing hsec when given "hhmmss" format

Signed-off-by: Ferry Huberts <f.huberts@mindef.nl>
tok: improve the nmea_calc_crc function a bit

Signed-off-by: Ferry Huberts <f.huberts@mindef.nl>