Fix release flags

flags were being accumulated instead of being set.
Win32 was getting -O2 -DNDEBUG -Ofast -DNDEBUG etc...
Also for Win32, stay compatible to WinXP

CMakeLists.txt

@@ -70,6 +70,9 @@ endif()
 if(WIN32 OR ARM7 OR ARM6)
   set(CMAKE_C_FLAGS_RELEASE "-O2 -DNDEBUG")
   set(CMAKE_CXX_FLAGS_RELEASE "-O2 -DNDEBUG")
+else()
+  set(CMAKE_C_FLAGS_RELEASE "-Ofast -DNDEBUG -Wno-unused-variable")
+  set(CMAKE_CXX_FLAGS_RELEASE "-Ofast -DNDEBUG -Wno-unused-variable")
 endif()
 
 # set this to 0 if per-block checkpoint needs to be disabled
@@ -310,6 +313,9 @@ else()
     # mingw doesn't support LTO (multiple definition errors at link time)
     set(USE_LTO_DEFAULT false)
     set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -Wl,--stack,10485760")
+    if(NOT BUILD_64)
+      add_definitions(-DWINVER=0x0501 -D_WIN32_WINNT=0x0501)
+    endif()
   endif()
   set(C_WARNINGS "-Waggregate-return -Wnested-externs -Wold-style-definition -Wstrict-prototypes")
   set(CXX_WARNINGS "-Wno-reorder -Wno-missing-field-initializers")
@@ -353,8 +359,6 @@ else()
     set(DEBUG_FLAGS "-g3 -O0")
   endif()
 
-  set(RELEASE_FLAGS "-Ofast -DNDEBUG -Wno-unused-variable")
-
   if(NOT DEFINED USE_LTO_DEFAULT)
     set(USE_LTO_DEFAULT true)
   endif()