Support for MSYS2

[tmssngr]

Please support building with MSYS2. Currently, I'm getting

$ make
cc -Wall -pedantic -g3 -DLIBPATH="\"/opt/fcc//lib\"" -DBINPATH="\"/opt/fcc//bin\""   -c -o cc.o cc.c
gcc -g3 cc.c -o cc
cc -Wall -pedantic -g3 -DLIBPATH="\"/opt/fcc//lib\"" -DBINPATH="\"/opt/fcc//bin\""   -c -o frontend.o frontend.c
frontend.c: In function ‘report’:
frontend.c:102:16: warning: implicit declaration of function ‘_itoa’; did you mean ‘_dtoa_r’? [-Wimplicit-function-declaration]
  102 |         writes(_itoa(line));
      |                ^~~~~
      |                _dtoa_r
frontend.c:102:16: warning: passing argument 1 of ‘writes’ makes pointer from integer without a cast [-Wint-conversion]
  102 |         writes(_itoa(line));
      |                ^~~~~~~~~~~
      |                |
      |                int
frontend.c:92:32: note: expected ‘const char *’ but argument is of type ‘int’
   92 | static void writes(const char *p)
      |                    ~~~~~~~~~~~~^
gcc -g3 frontend.o -o cc0
/usr/lib/gcc/x86_64-pc-msys/13.2.0/../../../../x86_64-pc-msys/bin/ld: frontend.o: in function `report':
/d/src/Fuzix-Compiler-Kit/frontend.c:102:(.text+0x137): undefined reference to `_itoa'
collect2: error: ld returned 1 exit status
make: *** [Makefile:76: cc0] Error 1