eal/windows: fix warnings

eal/windows: fix warnings

Fixed bunch of warnings when compiling using clang on Windows
such as the use of an unsafe string function (strerror),
[-Wunused-variable], [-Wunused-function] in eal_common_options.c
[-Wunused-const-variable] in getopt.c and [-Wunused-parameter]
in eal_common_thread.c.
Also fixed warnings generated using Mingw:
[-Werror=old-style-definition], [-Werror=cast-function-type] and
[-Werror=attributes]

Signed-off-by: Ranjit Menon <ranjit.menon@intel.com>
Signed-off-by: Pallavi Kadam <pallavi.kadam@intel.com>
Tested-by: Narcisa Vasile <navasile@linux.microsoft.com>
Acked-by: Narcisa Vasile <navasile@linux.microsoft.com>