app: fix plugin load on static builds

app: fix plugin load on static builds

When dpdk is compiled as static libraries, it is not possible
to load a plugin from an application. We get the following error:

  EAL: librte_pmd_xxxx.so: undefined symbol: per_lcore__rte_errno

This happens because the dpdk symbols are not exported. Add them to the
dynamic symbol table by using '-Wl,--export-dynamic'. This option was
previously present when compiled with Makefiles, it was introduced in
commit f9a08f650211 ("eal: add support for shared object drivers")

Fixes: 16ade738fd0d ("app/testpmd: build with meson")
Fixes: 89f0711f9ddf ("examples: build some samples with meson")
Cc: stable@dpdk.org
Signed-off-by: Olivier Matz <olivier.matz@6wind.com>