make the new --genDeps feature optional since it makes compilations slower

compiler/commands.nim

@@ -611,7 +611,7 @@ proc processSwitch(switch, arg: string, pass: TCmdLinePass, info: TLineInfo;
   of "skipparentcfg":
     expectNoArg(switch, arg, pass, info)
     incl(gGlobalOptions, optSkipParentConfigFiles)
-  of "genscript":
+  of "genscript", "gendeps":
     expectNoArg(switch, arg, pass, info)
     incl(gGlobalOptions, optGenScript)
   of "colors": processOnOffSwitchG({optUseColors}, arg, pass, info)

compiler/main.nim

@@ -80,6 +80,7 @@ proc commandCompileToC(graph: ModuleGraph; cache: IdentCache) =
     let proj = changeFileExt(gProjectFull, "")
     extccomp.callCCompiler(proj)
     extccomp.writeJsonBuildInstructions(proj)
+    if optGenScript in gGlobalOptions:
       writeDepsFile(graph, toGeneratedFile(proj, ""))
 
 proc commandJsonScript(graph: ModuleGraph; cache: IdentCache) =

doc/advopt.txt

@@ -37,6 +37,7 @@ Advanced options:
   --noMain                  do not generate a main procedure
   --genScript               generate a compile script (in the 'nimcache'
                             subdirectory named 'compile_$project$scriptext')
+  --genDeps                 generate a '.deps' file containing the dependencies
   --os:SYMBOL               set the target operating system (cross-compilation)
   --cpu:SYMBOL              set the target processor (cross-compilation)
   --debuginfo               enables debug information