Part numbers alone are ambiguous. I assume you mean the Intel 8031 aka the
MCS 51 family. No. There is no support for the Intel 8031. Support would
be impractical, as gcc isn't designed to support 8-bit microcontrollers.
While 8031/8051 processors are problematic I think your statement isn't
strictly correct - the AVR, 68HC11 and IP2022 are all 8-bit
microcontrollers (OK the marketing folks in the office will insist that
the IP2022 is an Internet Edge Processor, but it's still an 8-bit micro
and much like the 8031 has a single 8-bit accumulator :-)). gcc handles
these pretty nicely in fact. I can't remember but I had a feeling that
some of the H8 family are 8-bit too. IIRC someone posted a Z80 port
earlier this year too.