Cleaned up mmdisp.nim, moved implementations into lib/system/mm/ (#13254)

lib/system/mm/none.nim

@@ -0,0 +1,44 @@
+
+when appType == "lib":
+  {.warning: "nogc in a library context may not work".}
+
+include "system/alloc"
+
+proc initGC() = discard
+proc GC_disable() = discard
+proc GC_enable() = discard
+proc GC_fullCollect() = discard
+proc GC_setStrategy(strategy: GC_Strategy) = discard
+proc GC_enableMarkAndSweep() = discard
+proc GC_disableMarkAndSweep() = discard
+proc GC_getStatistics(): string = return ""
+
+proc newObj(typ: PNimType, size: int): pointer {.compilerproc.} =
+  result = alloc0Impl(size)
+
+proc newObjNoInit(typ: PNimType, size: int): pointer =
+  result = alloc(size)
+
+proc newSeq(typ: PNimType, len: int): pointer {.compilerproc.} =
+  result = newObj(typ, addInt(mulInt(len, typ.base.size), GenericSeqSize))
+  cast[PGenericSeq](result).len = len
+  cast[PGenericSeq](result).reserved = len
+
+proc growObj(old: pointer, newsize: int): pointer =
+  result = realloc(old, newsize)
+
+proc nimGC_setStackBottom(theStackBottom: pointer) = discard
+proc nimGCref(p: pointer) {.compilerproc, inline.} = discard
+proc nimGCunref(p: pointer) {.compilerproc, inline.} = discard
+
+proc unsureAsgnRef(dest: PPointer, src: pointer) {.compilerproc, inline.} =
+  dest[] = src
+proc asgnRef(dest: PPointer, src: pointer) {.compilerproc, inline.} =
+  dest[] = src
+proc asgnRefNoCycle(dest: PPointer, src: pointer) {.compilerproc, inline,
+  deprecated: "old compiler compat".} = asgnRef(dest, src)
+
+var allocator {.rtlThreadVar.}: MemRegion
+instantiateForRegion(allocator)
+
+include "system/cellsets"