OpenSSL: replace HUNTER_UWP_PLATFORM with direct CMAKE_SYSTEM_NAME ch…

…eck (#635)

replace HUNTER_UWP_PLATFORM with CMAKE_SYSTEM_NAME to follow CMake style.

Compare against `CMAKE_SYSTEM_NAME=WindowsStore` as described in CMake docs:
https://cmake.org/cmake/help/latest/manual/cmake-toolchains.7.html#cross-compiling-for-windows-store

cmake/projects/OpenSSL/schemes/url_sha1_openssl_windows_1_1_plus.cmake.in

@@ -63,13 +63,13 @@ endif()
 string(COMPARE EQUAL "@HUNTER_MSVC_ARCH_TARGET@" "amd64" is_amd64)
 string(COMPARE EQUAL "@HUNTER_MSVC_ARCH_TARGET@" "arm64" is_arm64)
 if(is_amd64 OR is_arm64)
-  if(HUNTER_UWP_PLATFORM)
+  if("${CMAKE_SYSTEM_NAME}" STREQUAL "WindowsStore")
     set(arch "VC-WIN64A-ONECORE")
   else()
     set(arch "VC-WIN64A")
   endif()
 else()
-  if(HUNTER_UWP_PLATFORM)
+  if("${CMAKE_SYSTEM_NAME}" STREQUAL "WindowsStore")
     set(arch "VC-WIN32-ONECORE")
   else() 
     set(arch "VC-WIN32")
@@ -80,7 +80,7 @@ if(DEBUG_RUNTIME)
   set(arch "debug-${arch}")
 endif()
 
-if(HUNTER_UWP_PLATFORM)
+if("${CMAKE_SYSTEM_NAME}" STREQUAL "WindowsStore")
   hunter_add_package(NASM) # set NASM_ROOT
   set(opt "no-async")
 elseif(ASM_SUPPORT)
@@ -105,7 +105,7 @@ else()
   set(shared "no-shared")
 endif()
 
-if(HUNTER_UWP_PLATFORM)
+if("${CMAKE_SYSTEM_NAME}" STREQUAL "WindowsStore")
   set(platform "store")
 else()
   set(platform "")