devel/arm-none-eabi-newlib: unbreak after include-fixed removal

We're now operating on more standards-compliant headers. Defining
__LONG_LONG_SUPPORTED is a little hacky, but some backflips are needed to
assume a C99 build. For now, just make it work so that we can get the
definition from sys/limits.h as needed.

MFH: 2020Q4 (blanket: build fix)