BUILD: Makefile: require SSL_LIB, SSL_INC to be explicitly set
The SSL_INC and SSL_LIB variables were not initialized in the Makefile,
so they could be accidently inherited from the environment. We require
that any makefile variable is explicitly set on the command line so they
must be initialized.
Note that the Travis scripts used to rely only on these variables to be
exported, so it was adjusted as well.
diff --git a/Makefile b/Makefile
index 2077ca8..3bfc84b 100644
--- a/Makefile
+++ b/Makefile
@@ -533,6 +533,8 @@
endif
ifneq ($(USE_OPENSSL),)
+SSL_INC =
+SSL_LIB =
# OpenSSL is packaged in various forms and with various dependencies.
# In general -lssl is enough, but on some platforms, -lcrypto may be needed,
# reason why it's added by default. Some even need -lz, then you'll need to