Allow Nimble to override the `task` template in nimscript. (#8798)

lib/system/nimscript.nim

@@ -305,7 +305,6 @@ template withDir*(dir: string; body: untyped): untyped =
   finally:
     cd(curDir)
 
-template `==?`(a, b: string): bool = cmpIgnoreStyle(a, b) == 0
 
 proc writeTask(name, desc: string) =
   if desc.len > 0:
@@ -313,7 +312,14 @@ proc writeTask(name, desc: string) =
     for i in 0 ..< 20 - name.len: spaces.add ' '
     echo name, spaces, desc
 
-template task*(name: untyped; description: string; body: untyped): untyped =
+proc cppDefine*(define: string) =
+  ## tell Nim that ``define`` is a C preprocessor ``#define`` and so always
+  ## needs to be mangled.
+  builtin
+
+when not defined(nimble):
+  template `==?`(a, b: string): bool = cmpIgnoreStyle(a, b) == 0
+  template task*(name: untyped; description: string; body: untyped): untyped =
     ## Defines a task. Hidden tasks are supported via an empty description.
     ## Example:
     ##
@@ -330,12 +336,6 @@ template task*(name: untyped; description: string; body: untyped): untyped =
       setCommand "nop"
       `name Task`()
 
-proc cppDefine*(define: string) =
-  ## tell Nim that ``define`` is a C preprocessor ``#define`` and so always
-  ## needs to be mangled.
-  builtin
-
-when not defined(nimble):
   # nimble has its own implementation for these things.
   var
     packageName* = ""    ## Nimble support: Set this to the package name. It