pmdinfogen: fix build warnings

pmdinfogen: fix build warnings

When compiled with a standard clang, pmdinfogen can raise a warning:
    buildtools/pmdinfogen/pmdinfogen.c:365:1: warning:
    control reaches end of non-void function

Actually there can be more warnings with stricter compilers.
In order to catch them early and fix most of them, the DPDK standard flags
WERROR_FLAGS are used.

The warnings fixed are:
    no previous prototype for ...
    no return statement in function returning non-void
    variable ‘secstrings’ set but not used
    ‘sec_name’ defined but not used
    ‘get_symbol_index’ defined but not used
    pointer of type ‘void *’ used in arithmetic

Fixes: 98b0fdb0ffc6 ("pmdinfogen: add buildtools and pmdinfogen utility")

Signed-off-by: Thomas Monjalon <thomas.monjalon@6wind.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>