use non-Cellar OpenSSL path for macOS

removes the dependency on a specific version, as long as the installed
version is 1.0.x. Also set the appropriate environment flags for OpenSSL
 on macOS.

Note: the setting of these two environment variables would be better
suited to a user's `~/.bash_profile` rather than being done within
CMake, as doing it here is destructive.

CMakeLists.txt

@@ -2,7 +2,6 @@ cmake_minimum_required(VERSION 3.10)
 project(PIVX)
 
 set(BDB_VER "4.8.30")
-set(OPENSSL_VER "1.0.2r")
 set(CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/contrib/cmake")
 set(CMAKE_CXX_STANDARD 11)
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 ")
@@ -11,9 +10,11 @@ include(${CMAKE_ROOT}/Modules/ExternalProject.cmake)
 if(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
     message(STATUS "Compiling on macOS")
     list(APPEND CMAKE_PREFIX_PATH /usr/local/opt/qt5)
-    list(APPEND CMAKE_PREFIX_PATH /usr/local/Cellar/openssl/${OPENSSL_VER})
+    list(APPEND CMAKE_PREFIX_PATH /usr/local/opt/openssl)
     list(APPEND CMAKE_PREFIX_PATH /usr/local/Cellar/berkeley-db@4)
-    set(OPENSSL_ROOT_DIR "/usr/local/Cellar/openssl/${OPENSSL_VER}/")
+    set(OPENSSL_ROOT_DIR "/usr/local/opt/openssl/")
+    set(ENV{CPPFLAGS} "-I${OPENSSL_ROOT_DIR}/include")
+    set(ENV{LDFLAGS} "-L${OPENSSL_ROOT_DIR}/lib")
     set(BerkeleyDB_ROOT_DIR "/usr/local/Cellar/berkeley-db@4/${BDB_VER}/")
 elseif(${CMAKE_SYSTEM_NAME} MATCHES "Linux")
     file(READ "/proc/version" _SYS_VERSION)