Add staticFileExists and staticDirExists (#22278)

lib/std/staticos.nim

@@ -0,0 +1,13 @@
+## This module implements path handling like os module but works at only compile-time.
+## This module works even when cross compiling to OS that is not supported by os module.
+
+proc staticFileExists*(filename: string): bool {.compileTime.} =
+  ## Returns true if `filename` exists and is a regular file or symlink.
+  ##
+  ## Directories, device files, named pipes and sockets return false.
+  discard
+
+proc staticDirExists*(dir: string): bool {.compileTime.} =
+  ## Returns true if the directory `dir` exists. If `dir` is a file, false
+  ## is returned. Follows symlinks.
+  discard