fix custom pragma with backticks not working [backport] (#24151)

refs https://forum.nim-lang.org/t/12522

compiler/pragmas.nim

@@ -800,13 +800,14 @@ proc pragmaGuard(c: PContext; it: PNode; kind: TSymKind): PSym =
 proc semCustomPragma(c: PContext, n: PNode, sym: PSym): PNode =
   var callNode: PNode
 
-  if n.kind in {nkIdent, nkSym}:
+  case n.kind
+  of nkIdentKinds:
     # pragma -> pragma()
     callNode = newTree(nkCall, n)
-  elif n.kind == nkExprColonExpr:
+  of nkExprColonExpr:
     # pragma: arg -> pragma(arg)
     callNode = newTree(nkCall, n[0], n[1])
-  elif n.kind in nkPragmaCallKinds:
+  of nkPragmaCallKinds - {nkExprColonExpr}:
     callNode = n
   else:
     invalidPragma(c, n)

tests/pragmas/tcustom_pragma.nim

@@ -531,3 +531,10 @@ block:
 
   check(a)
   check(b)
+
+block: # https://forum.nim-lang.org/t/12522, backticks
+  template `mypragma`() {.pragma.}
+  # Error: invalid pragma: `mypragma`
+  type Test = object
+    field {.`mypragma`.}: int
+  doAssert Test().field.hasCustomPragma(mypragma)