Initial TLS support.

cmake/OpenSSL.cmake

@@ -0,0 +1,18 @@
+if (WITH_TLS)
+    set(OPENSSL_ROOT_DIR ${XMRIG_DEPS})
+    set(OPENSSL_USE_STATIC_LIBS TRUE)
+    set(OPENSSL_MSVC_STATIC_RT TRUE)
+
+    find_package(OpenSSL)
+
+    if (OPENSSL_FOUND)
+        set(TLS_SOURCES src/common/net/Tls.h src/common/net/Tls.cpp)
+        include_directories(${OPENSSL_INCLUDE_DIR})
+    else()
+        message(FATAL_ERROR "OpenSSL NOT found: use `-DWITH_TLS=OFF` to build without TLS support")
+    endif()
+else()
+    set(TLS_SOURCES "")
+    set(OPENSSL_LIBRARIES "")
+    add_definitions(/DXMRIG_NO_TLS)
+endif()