Introduce first class support for Android (#5772)

lib/pure/ospaths.nim

@@ -528,11 +528,26 @@ when declared(getEnv) or defined(nimscript):
     elif getEnv("XDG_CONFIG_DIR"): return string(getEnv("XDG_CONFIG_DIR")) & "/"
     else: return string(getEnv("HOME")) & "/.config/"
 
+  when defined(android):
+    {.pragma: getTempDirEffects, tags: [ReadEnvEffect, ReadIOEffect, WriteDirEffect].}
+  elif defined(windows):
+    {.pragma: getTempDirEffects, tags: [ReadEnvEffect, ReadIOEffect].}
+  else:
+    {.pragma: getTempDirEffects, tags: [ReadIOEffect].}
+
   proc getTempDir*(): string {.rtl, extern: "nos$1",
-    tags: [ReadEnvEffect, ReadIOEffect].} =
+    getTempDirEffects.} =
     ## Returns the temporary directory of the current user for applications to
     ## save temporary files in.
-    when defined(windows): return string(getEnv("TEMP")) & "\\"
+    when defined(tempDir):
+      const tempDir {.strdefine.}: string = nil
+      return tempDir
+    elif defined(windows): return string(getEnv("TEMP")) & "\\"
+    elif defined(android):
+      let tempDir = getHomeDir() / "nimtempfs"
+      try: createDir(tempDir)
+      except OSError: discard
+      return tempDir
     else: return "/tmp/"
 
   proc expandTilde*(path: string): string {.