-Werror,-Wdeprecated-volatile (clang-cl)

same as b89187aad8 "Simplify forced memory reads"
in sal/osl/unx/file.cxx

Change-Id: I31edbc72f88895e148609498d367a50e38723b11
Reviewed-on: https://gerrit.libreoffice.org/81408
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

sal/osl/w32/file.cxx

@@ -777,19 +777,18 @@ oslFileError SAL_CALL osl_mapFile(
          * Pagein, touching first byte of each memory page.
          * Note: volatile disables optimizing the loop away.
          */
-        BYTE * pData(static_cast<BYTE*>(*ppAddr));
+        BYTE volatile * pData(static_cast<BYTE*>(*ppAddr));
         SIZE_T nSize(nLength);
 
-        volatile BYTE c = 0;
         while (nSize > dwPageSize)
         {
-            c ^= pData[0];
+            pData[0];
             pData += dwPageSize;
             nSize -= dwPageSize;
         }
         if (nSize > 0)
         {
-            c ^= pData[0];
+            pData[0];
         }
     }
     return osl_File_E_None;