Use `Base.o_*` instead of raw `{#const O_*}`

`stage1` cross compilers could use different values instead of
system-defined. GHC JS Backend change these constants to be compatible
with Node.js environment.

System/Posix/IO/Common.hsc

@@ -223,12 +223,18 @@ openat_ fdMay str how (OpenFileFlags appendFlag exclusiveFlag nocttyFlag
     c_fd = maybe (#const AT_FDCWD) (\ (Fd fd) -> fd) fdMay
     all_flags  = creat .|. flags .|. open_mode
 
+    -- We have to use Base.o_* instead of raw #const O_*
+    -- due of the fact target platforms at stage1 could have
+    -- them overridden.
+    -- For example GHC JS Backend provides its own constants
+    -- which should be used at the target of cross compilation
+    -- into Node.JS environment.
     flags =
-       (if appendFlag       then (#const O_APPEND)    else 0) .|.
-       (if exclusiveFlag    then (#const O_EXCL)      else 0) .|.
-       (if nocttyFlag       then (#const O_NOCTTY)    else 0) .|.
-       (if nonBlockFlag     then (#const O_NONBLOCK)  else 0) .|.
-       (if truncateFlag     then (#const O_TRUNC)     else 0) .|.
+       (if appendFlag       then (Base.o_APPEND)      else 0) .|.
+       (if exclusiveFlag    then (Base.o_EXCL)        else 0) .|.
+       (if nocttyFlag       then (Base.o_NOCTTY)      else 0) .|.
+       (if nonBlockFlag     then (Base.o_NONBLOCK)    else 0) .|.
+       (if truncateFlag     then (Base.o_TRUNC)       else 0) .|.
        (if nofollowFlag     then (#const O_NOFOLLOW)  else 0) .|.
        (if cloexecFlag      then (#const O_CLOEXEC)   else 0) .|.
        (if directoryFlag    then (#const O_DIRECTORY) else 0) .|.
@@ -236,12 +242,12 @@ openat_ fdMay str how (OpenFileFlags appendFlag exclusiveFlag nocttyFlag
 
     (creat, mode_w) = case creatFlag of
                         Nothing -> (0,0)
-                        Just x  -> ((#const O_CREAT), x)
+                        Just x  -> ((Base.o_CREAT), x)
 
     open_mode = case how of
-                   ReadOnly  -> (#const O_RDONLY)
-                   WriteOnly -> (#const O_WRONLY)
-                   ReadWrite -> (#const O_RDWR)
+                   ReadOnly  -> (Base.o_RDONLY)
+                   WriteOnly -> (Base.o_WRONLY)
+                   ReadWrite -> (Base.o_RDWR)
 
 foreign import capi unsafe "HsUnix.h openat"
    c_openat :: CInt -> CString -> CInt -> CMode -> IO CInt
@@ -315,8 +321,8 @@ data FdOption = AppendOnWrite     -- ^O_APPEND
 
 fdOption2Int :: FdOption -> CInt
 fdOption2Int CloseOnExec       = (#const FD_CLOEXEC)
-fdOption2Int AppendOnWrite     = (#const O_APPEND)
-fdOption2Int NonBlockingRead   = (#const O_NONBLOCK)
+fdOption2Int AppendOnWrite     = (Base.o_APPEND)
+fdOption2Int NonBlockingRead   = (Base.o_NONBLOCK)
 fdOption2Int SynchronousWrites = (#const O_SYNC)
 
 -- | May throw an exception if this is an invalid descriptor.

System/Posix/Semaphore.hsc

@@ -30,6 +30,7 @@ import Foreign.ForeignPtr hiding (newForeignPtr)
 import Foreign.Concurrent
 import Foreign.Ptr
 import System.Posix.Types
+import qualified System.Posix.Internals as Base
 import Control.Concurrent
 import Data.Bits
 #if !defined(HAVE_SEM_GETVALUE)
@@ -61,11 +62,11 @@ newtype Semaphore = Semaphore (ForeignPtr ())
 --   value.
 semOpen :: String -> OpenSemFlags -> FileMode -> Int -> IO Semaphore
 semOpen name flags mode value =
-    let cflags = (if semCreate flags then #{const O_CREAT} else 0) .|.
-                 (if semExclusive flags then #{const O_EXCL} else 0)
+    let cflags = (if semCreate flags then Base.o_CREAT else 0) .|.
+                 (if semExclusive flags then Base.o_EXCL else 0)
         semOpen' cname =
             do sem <- throwErrnoPathIfNull "semOpen" name $
-                      sem_open cname (toEnum cflags) mode (toEnum value)
+                      sem_open cname (toEnum (fromIntegral cflags)) mode (toEnum value)
                fptr <- newForeignPtr sem (finalize sem)
                return $ Semaphore fptr
         finalize sem = throwErrnoPathIfMinus1_ "semOpen" name $

System/Posix/SharedMem.hsc

@@ -26,6 +26,7 @@ module System.Posix.SharedMem
 #include <fcntl.h>
 
 import System.Posix.Types
+import qualified System.Posix.Internals as Base
 #if defined(HAVE_SHM_OPEN) || defined(HAVE_SHM_UNLINK)
 import Foreign.C
 #endif
@@ -50,14 +51,14 @@ shmOpen :: String -> ShmOpenFlags -> FileMode -> IO Fd
 shmOpen name flags mode =
     do cflags0 <- return 0
        cflags1 <- return $ cflags0 .|. (if shmReadWrite flags
-                                        then #{const O_RDWR}
-                                        else #{const O_RDONLY})
-       cflags2 <- return $ cflags1 .|. (if shmCreate flags then #{const O_CREAT}
+                                        then Base.o_RDWR
+                                        else Base.o_RDONLY)
+       cflags2 <- return $ cflags1 .|. (if shmCreate flags then Base.o_CREAT
                                         else 0)
        cflags3 <- return $ cflags2 .|. (if shmExclusive flags
-                                        then #{const O_EXCL}
+                                        then Base.o_EXCL
                                         else 0)
-       cflags4 <- return $ cflags3 .|. (if shmTrunc flags then #{const O_TRUNC}
+       cflags4 <- return $ cflags3 .|. (if shmTrunc flags then Base.o_TRUNC
                                         else 0)
        withCAString name (shmOpen' cflags4)
     where shmOpen' cflags cname =