revert second argument of inc not being generic (#24129)

refs #22328, fixes regression in
https://forum.nim-lang.org/t/12465#76998

lib/system/arithmetics.nim

@@ -1,4 +1,4 @@
-proc succ*[T: Ordinal](x: T, y: int = 1): T {.magic: "Succ", noSideEffect.} =
+proc succ*[T, V: Ordinal](x: T, y: V = 1): T {.magic: "Succ", noSideEffect.} =
   ## Returns the `y`-th successor (default: 1) of the value `x`.
   ##
   ## If such a value does not exist, `OverflowDefect` is raised
@@ -7,7 +7,7 @@ proc succ*[T: Ordinal](x: T, y: int = 1): T {.magic: "Succ", noSideEffect.} =
     assert succ(5) == 6
     assert succ(5, 3) == 8
 
-proc pred*[T: Ordinal](x: T, y: int = 1): T {.magic: "Pred", noSideEffect.} =
+proc pred*[T, V: Ordinal](x: T, y: V = 1): T {.magic: "Pred", noSideEffect.} =
   ## Returns the `y`-th predecessor (default: 1) of the value `x`.
   ##
   ## If such a value does not exist, `OverflowDefect` is raised
@@ -16,7 +16,7 @@ proc pred*[T: Ordinal](x: T, y: int = 1): T {.magic: "Pred", noSideEffect.} =
     assert pred(5) == 4
     assert pred(5, 3) == 2
 
-proc inc*[T: Ordinal](x: var T, y: int = 1) {.magic: "Inc", noSideEffect.} =
+proc inc*[T, V: Ordinal](x: var T, y: V = 1) {.magic: "Inc", noSideEffect.} =
   ## Increments the ordinal `x` by `y`.
   ##
   ## If such a value does not exist, `OverflowDefect` is raised or a compile
@@ -28,7 +28,7 @@ proc inc*[T: Ordinal](x: var T, y: int = 1) {.magic: "Inc", noSideEffect.} =
     inc(i, 3)
     assert i == 6
 
-proc dec*[T: Ordinal](x: var T, y: int = 1) {.magic: "Dec", noSideEffect.} =
+proc dec*[T, V: Ordinal](x: var T, y: V = 1) {.magic: "Dec", noSideEffect.} =
   ## Decrements the ordinal `x` by `y`.
   ##
   ## If such a value does not exist, `OverflowDefect` is raised or a compile

tests/int/tunsignedinc.nim

@@ -32,3 +32,9 @@ block t4175:
   const j = 0u - 1u
   doAssert i == j
   doAssert j + 1u == 0u
+
+block: # https://forum.nim-lang.org/t/12465#76998
+  var a: int = 1
+  var x: uint8 = 1
+  a.inc(x)   # Error: type mismatch
+  doAssert a == 2

tests/varres/tprevent_forloopvar_mutations.nim

@@ -2,7 +2,7 @@ discard """
   errormsg: "type mismatch: got <int>"
   nimout: '''tprevent_forloopvar_mutations.nim(16, 3) Error: type mismatch: got <int>
 but expected one of:
-proc inc[T: Ordinal](x: var T; y: int = 1)
+proc inc[T, V: Ordinal](x: var T; y: V = 1)
   first type mismatch at position: 1
   required type for x: var T: Ordinal
   but expression 'i' is immutable, not 'var'