Fix option name in winconf-xxx.cmake

The mistake was made by commit 7712d0ada0

cmake/Modules/winconf-mingw.cmake

@@ -1,9 +1,9 @@
-if (STACKTRACE_WIN)
+if (STACKTRACE)
     if ("${WINXXBITS}" NOT STREQUAL "Win64")
         add_compile_options(-fno-omit-frame-pointer)
     endif ("${WINXXBITS}" NOT STREQUAL "Win64")
     link_libraries(libdbghelp  -Wl,--export-all-symbols)
-endif (STACKTRACE_WIN)
+endif (STACKTRACE)
 
 if (("${CMAKE_BUILD_TYPE}" STREQUAL "Debug") OR ("${CMAKE_BUILD_TYPE}" STREQUAL "RelWithDebInfo"))
     link_libraries(-Wl,--dynamicbase)

cmake/Modules/winconf-msvc.cmake

@@ -1,4 +1,4 @@
-if (STACKTRACE_WIN)
+if (STACKTRACE)
     if ("${WINXXBITS}" STREQUAL "Win64")
         add_compile_options(-Zi)
     else ("${WINXXBITS}" STREQUAL "Win64")
@@ -6,7 +6,7 @@ if (STACKTRACE_WIN)
         add_compile_options(-Oy-)
     endif ("${WINXXBITS}" STREQUAL "Win64")
     link_libraries(dbghelp.lib)
-endif (STACKTRACE_WIN)
+endif (STACKTRACE)
 
 # Enable Wide characters
 add_definitions(-DTORRENT_USE_WPATH)