eal: disable syslog and dlopen on Windows

eal: disable syslog and dlopen on Windows

Excluding syslog/ dlfcn definitions and parameters
from Windows by adding #ifndef RTE_EXEC_ENV_WINDOWS.

Note: This is a temporary change. In future, separate
'unix' directory will be created for unix specific functions.

Signed-off-by: Pallavi Kadam <pallavi.kadam@intel.com>
Reviewed-by: Ranjit Menon <ranjit.menon@intel.com>
Reviewed-by: Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>
Tested-by: Narcisa Ana Maria Vasile <narcisa.vasile@microsoft.com>
Acked-by: Narcisa Ana Maria Vasile <narcisa.vasile@microsoft.com>