ext: lib: tinycbor: half/full-FP support changes

- Make half float encode/decode conditional
- src/cborpretty.c, src/cbortojson.c and src/cborvalidation.c
  conditionally include math.h and half float type support
- Conditionally include math.h in src/compilersupport_p.h to avoid
  newlib libc from getting compiled in
- Conditionally compile src/cborparser_dup_string.c if newlib libc is
  compiled in

Signed-off-by: Vipul Rahane <vipulrahane@apache.org>