Fix static link with openssl

Recent versions of cmake stopped linking with -ldl implicitely,
which may be required when linking statically with openssl.
However this can still be done using find_package(OpenSSL) by
setting OPENSSL_USE_STATIC_LIBS to TRUE.

Configure.cmake

@@ -13,6 +13,9 @@ endif()
 
 set(OPENSSL_EXTRA_LIBRARIES "" CACHE STRING "Extra libraries for openssl")
 if (NOT CMAKE_CROSSCOMPILING AND NOT SLEEF_FORCE_FIND_PACKAGE_SSL)
+  if (SLEEF_BUILD_STATIC_TEST_BINS)
+    set(OPENSSL_USE_STATIC_LIBS TRUE)
+  endif()
   find_package(OpenSSL)
   if (OPENSSL_FOUND)
     set(SLEEF_OPENSSL_FOUND TRUE)