more checking for --gc:arc, no need for valgrind (#14467)

* sigmatch: removed dead code

lib/system/mmdisp.nim

@@ -38,27 +38,10 @@ type
   PByte = ptr ByteArray
   PString = ptr string
 
-# Page size of the system; in most cases 4096 bytes. For exotic OS or
-# CPU this needs to be changed:
-const
-  PageShift = when defined(cpu16): 8 else: 12 # \
-    # my tests showed no improvements for using larger page sizes.
-  PageSize = 1 shl PageShift
-  PageMask = PageSize-1
-
-  MemAlign = 16 # also minimal allocatable memory block
-
-  BitsPerPage = PageSize div MemAlign
-  UnitsPerPage = BitsPerPage div (sizeof(int)*8)
-    # how many ints do we need to describe a page:
-    # on 32 bit systems this is only 16 (!)
-
-  TrunkShift = 9
-  BitsPerTrunk = 1 shl TrunkShift # needs to be power of 2 and divisible by 64
-  TrunkMask = BitsPerTrunk - 1
-  IntsPerTrunk = BitsPerTrunk div (sizeof(int)*8)
-  IntShift = 5 + ord(sizeof(int) == 8) # 5 or 6, depending on int width
-  IntMask = 1 shl IntShift - 1
+when declared(IntsPerTrunk):
+  discard
+else:
+  include bitmasks
 
 proc raiseOutOfMem() {.noinline.} =
   if outOfMemHook != nil: outOfMemHook()