unix: be more explicit about target triple when building OpenSSL

This is more robust when more targets will be supported.

Author: indygreg

cpython-unix/build-openssl.sh

@@ -25,8 +25,11 @@ fi
 
 if [ "${PYBUILD_PLATFORM}" = "macos" ]; then
   OPENSSL_TARGET=darwin64-x86_64-cc
-else
+elif [ "${TARGET_TRIPLE}" = "x86_64-unknown-linux-gnu" ]; then
   OPENSSL_TARGET=linux-x86_64
+else
+   echo "Error: unsupported target"
+   exit 1
 fi
 
 /usr/bin/perl ./Configure --prefix=/tools/deps ${OPENSSL_TARGET} no-shared ${EXTRA_FLAGS}