Help assemble the released GW-BASIC source code

It does minimal source modifications by using older MASM versions.

There are 63 missing symbols: CLREOL CLRSCN CSRATR CSRDSP DONOTE DOWNC EDTMAP FETCHC FKYADV FKYFMT GETFBC GETHED GRPSIZ GTASPC GWINI GWTERM INFMAP INICOM INKMAP KEYINP LCPY LEFTC MAPSUP MAPXYC NREAD NSETCX NWRITE PEKFLT PGINIT PIXSIZ PNTINI POKFLT POLLEV PRTMAP RDPEN RDSTIK RDTRIG READC RECCOM RIGHTC SCALXY SCANL SCANR SCRATR SCRINP SCROLL SCROUT SCRSTT SEGINI SETATR SETC SETCBF SETCLR SETFBC SNDCOM SNDLPT STACOM STOREC SWIDTH TDOWNC TRMCOM TUPC UPC