base: Use strerror_r

As noted by #24344, `strerror` is not necessarily thread-safe.
Thankfully, POSIX.1-2001 has long offered `strerror_r`, which is
safe to use.

Fixes #24344.

libraries/base/cbits/strerror.c

+// glibc will only expose the POSIX strerror_r if this is defined.
+#define _POSIX_C_SOURCE 200112L
+
+#include <string.h>
+
+int base_strerror_r(int errnum, char *ptr, size_t buflen)
+{
+    return strerror_r(errnum, ptr, buflen);
+}

libraries/base/src/Foreign/C/Error.hs

@@ -460,6 +460,20 @@ throwErrnoPathIfMinus1_  = throwErrnoPathIf_ (== -1)
 -- conversion of an "errno" value into IO error
 -- --------------------------------------------
 
+foreign import ccall "base_strerror_r"
+    c_strerror_r :: CInt -> Ptr CChar -> CSize -> IO CInt
+
+errnoToString :: Errno -> IO String
+errnoToString errno =
+    allocaBytes len $ \ptr -> do
+        ret <- c_strerror_r errno ptr len
+        if ret /= 0
+          then return "errnoToString failed"
+          else peekCString ptr
+  where
+    len :: Num a => a
+    len = 512
+
 -- | Construct an 'IOError' based on the given 'Errno' value.
 -- The optional information can be used to improve the accuracy of
 -- error messages.
@@ -470,7 +484,7 @@ errnoToIOError  :: String       -- ^ the location where the error occurred
                 -> Maybe String -- ^ optional filename associated with the error
                 -> IOError
 errnoToIOError loc errno maybeHdl maybeName = unsafePerformIO $ do
-    str <- strerror errno >>= peekCString
+    str <- errnoToString errno
     return (IOError maybeHdl errType loc str (Just errno') maybeName)
     where
     Errno errno' = errno
@@ -576,5 +590,3 @@ errnoToIOError loc errno maybeHdl maybeName = unsafePerformIO $ do
         | errno == eXDEV           = UnsupportedOperation
         | otherwise                = OtherError
 
-foreign import ccall unsafe "string.h" strerror :: Errno -> IO (Ptr CChar)
-