Fix WASI build

The `System.Posix.Files.PosixString` and `System.Posix.Temp.PosixString`
modules failed to build on the WASI/WASM platform because foreign
imports of `mkstemp` and `mknod` was not conditional on `configure`
findings.

This patch aligns these modules with their non-`PosixString`
counterparts.

See: #245
See: https://github.com/haskell/unix/runs/8284652815?check_suite_focus=true

Author: NicolasT

System/Posix/Files/PosixString.hsc

@@ -107,6 +107,11 @@ import System.Posix.PosixPath.FilePath
 
 import Data.Time.Clock.POSIX (POSIXTime)
 
+#if !defined(HAVE_MKNOD)
+import System.IO.Error ( ioeSetLocation )
+import GHC.IO.Exception ( unsupportedOperation )
+#endif
+
 -- -----------------------------------------------------------------------------
 -- chmod()
 
@@ -205,6 +210,13 @@ createNamedPipe name mode = do
   withFilePath name $ \s ->
     throwErrnoPathIfMinus1_ "createNamedPipe" name (c_mkfifo s mode)
 
+#if !defined(HAVE_MKNOD)
+
+{-# WARNING createDevice "operation will throw 'IOError' \"unsupported operation\" (CPP guard: @#if HAVE_MKNOD@)" #-}
+createDevice :: PosixPath -> FileMode -> DeviceID -> IO ()
+createDevice _ _ _ = ioError (ioeSetLocation unsupportedOperation "createDevice")
+
+#else
 -- | @createDevice path mode dev@ creates either a regular or a special file
 -- depending on the value of @mode@ (and @dev@).  @mode@ will normally be either
 -- 'blockSpecialMode' or 'characterSpecialMode'.  May fail with
@@ -221,6 +233,8 @@ createDevice path mode dev =
 foreign import capi unsafe "HsUnix.h mknod"
   c_mknod :: CString -> CMode -> CDev -> IO CInt
 
+#endif // HAVE_MKNOD
+
 -- -----------------------------------------------------------------------------
 -- Hard links
 

System/Posix/Temp/PosixString.hsc

@@ -35,6 +35,19 @@ import System.Posix.Directory.PosixPath (createDirectory)
 import System.Posix.IO.PosixString
 import System.Posix.Types
 
+#if !defined(HAVE_MKSTEMP)
+import System.IO.Error ( ioeSetLocation )
+import GHC.IO.Exception ( unsupportedOperation )
+#endif
+
+#if !defined(HAVE_MKSTEMP)
+
+{-# WARNING mkstemp "operation will throw 'IOError' \"unsupported operation\" (CPP guard: @#if HAVE_MKSTEMP@)" #-}
+mkstemp :: PosixString -> IO (PosixPath, Handle)
+mkstemp _ = ioError (ioeSetLocation unsupportedOperation "mkstemp")
+
+#else
+
 foreign import capi unsafe "HsUnix.h mkstemp"
   c_mkstemp :: CString -> IO CInt
 
@@ -54,6 +67,8 @@ mkstemp (PosixString template') = do
     h <- fdToHandle (Fd fd)
     return (name, h)
 
+#endif // HAVE_MKSTEMP
+
 #if HAVE_MKSTEMPS
 foreign import capi unsafe "HsUnix.h mkstemps"
   c_mkstemps :: CString -> CInt -> IO CInt