package/libopenssl: fix static build

no-dso option has been removed with
https://github.com/openssl/openssl/commit/31b6ed76dfd53529b74e79830c81372d0b756929

To fix this error, use "gcc" target in static builds. This target is
very minimalistic, we need to manually pass -lpthread and
-DOPENSSL_THREADS however we can also remove libdl workarounds

Fixes:
 - http://autobuild.buildroot.org/results/96d6b89d20980e8f7fa450b832474a81d492b315



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>