Define owcc (OpenWatcom C compiler) as a supported compiler.

This is a much better idea than simply changing the the `gcc` binary
to be `owcc`, since OpenWatcom does not support certain features such
as case ranges. `$nim/config/nim.cfg` has been updated to reflect this
change. The proper memory model is also now automatically selected for
the `i086` and `i086big` CPU targets and `-bdos` is also automatically
passed to the C compiler.

compiler/extccomp.nim

@@ -242,6 +242,32 @@ compiler tcc:
     cppXsupport: "",
     props: {hasSwitchRange, hasComputedGoto, hasGnuAsm})
 
+# OpenWatcom C Compiler
+compiler owcc:
+  result = (
+    name: "owcc",
+    objExt: "o",
+    optSpeed: " -O3",
+    optSize: " -Os",
+    compilerExe: "owcc",
+    cppCompiler: "owcc",
+    compileTmpl: "-c $options $include -o $objfile $file",
+    buildGui: " -mwindows",
+    buildDll: " -shared",
+    buildLib: "wlib $libfile $objfiles",
+    linkerExe: "",
+    linkTmpl: "$buildgui $builddll -o $exefile $objfiles $options",
+    includeCmd: " -I",
+    linkDirCmd: " -L",
+    linkLibCmd: " -l$1",
+    debug: "",
+    pic: "",
+    asmStmtFrmt: "$1 $2",
+    structStmtFmt: "$1 $2", # struct|union [packed] $name
+    produceAsm: gnuAsmListing,
+    cppXsupport: "",
+    props: {hasGnuAsm})
+
 # Your C Compiler
 compiler envcc:
   result = (
@@ -280,7 +306,8 @@ const
     envcc(),
     icl(),
     icc(),
-    clangcl()]
+    clangcl(),
+    owcc()]
 
   hExt* = ".h"
 

compiler/options.nim

@@ -231,7 +231,7 @@ type
 
   TSystemCC* = enum
     ccNone, ccGcc, ccNintendoSwitch, ccLLVM_Gcc, ccCLang, ccBcc, ccVcc,
-    ccTcc, ccEnv, ccIcl, ccIcc, ccClangCl
+    ccTcc, ccEnv, ccIcl, ccIcc, ccClangCl, ccOwcc
 
   ExceptionSystem* = enum
     excNone,   # no exception system selected yet

config/nim.cfg

@@ -33,12 +33,6 @@ riscv32.linux.gcc.exe = "riscv64-linux-gnu-gcc"
 riscv32.linux.gcc.linkerexe = "riscv64-linux-gnu-gcc"
 riscv64.linux.gcc.exe = "riscv64-linux-gnu-gcc"
 riscv64.linux.gcc.linkerexe = "arm-linux-gnueabihf-gcc"
-# 16-bit x86, e.g. 8086: OpenWatcom compiler
-i086.dos.gcc.exe = "owcc"
-i086.dos.gcc.linkerexe = "owcc"
-# 16-bit x86, but with large/huge code and data model
-i086big.dos.gcc.exe = "owcc"
-i086big.dos.gcc.linkerexe = "owcc"
 
 # For OpenWRT, you will also need to adjust PATH to point to your toolchain.
 mips.linux.gcc.exe = "mips-openwrt-linux-gcc"
@@ -99,6 +93,20 @@ nimblepath="$home/.nimble/pkgs/"
   gcc.options.always %= "${gcc.options.always} -fsanitize=null -fsanitize-undefined-trap-on-error"
 @end
 
+@if (i086 or i086big) and dos:
+  # Cross compile for DOS using OpenWatcom
+  cc = owcc
+  owcc.options.always %= "${owcc.options.always} -bdos"
+  owcc.options.linker %= "${owcc.options.linker} -bdos"
+  @if hugeModel:
+    owcc.options.always %= "${owcc.options.always} -mcmodel=h"
+  @elif largeModel or i086big:
+    owcc.options.always %= "${owcc.options.always} -mcmodel=l"
+  @elif smallModel or i086:
+    owcc.options.always %= "${owcc.options.always} -mcmodel=s"
+  @end
+@end
+
 @if unix and mingw:
   # Cross compile for Windows from Linux/OSX using MinGW
   i386.windows.gcc.exe = "i686-w64-mingw32-gcc"