Silence upcoming GCC 8 -Werror=sizeof-pointer-memaccess

...("error: argument to ‘sizeof’ in ‘char* strncpy(char*, const char*, size_t)’
call is the same expression as the source; did you mean to use the size of the
destination?") in a place where the use of strncpy instead of strcpy (introduced
with 9276f7d5 "fdo#32263") doesn't help prevent
any buffer overflows anyway (the target's size already having been checked to be
sufficiently large).

Change-Id: I70773538f4092f1306fb00f1fa7f9138e06894e5
Reviewed-on: https://gerrit.libreoffice.org/48391Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

sal/osl/unx/security.cxx

@@ -365,7 +365,7 @@ static bool osl_psz_getConfigDir(oslSecurity Security, sal_Char* pszDirectory, s
         n = strlen(pszDirectory);
         if (n + sizeof(DOT_CONFIG) < nMax)
         {
-            strncpy(pszDirectory+n, DOT_CONFIG, sizeof(DOT_CONFIG));
+            strcpy(pszDirectory+n, DOT_CONFIG); // safe
 
             // try to create dir if not present
             bool dirOK = true;