cmake: do not pass -O2 in debug build on ARM

Also, minor cleanup of redundant flag-setting code.

CMakeLists.txt

@@ -73,13 +73,14 @@ if (NOT "${ARCH}" STREQUAL "")
 endif()
 
 if(WIN32 OR ARM7 OR ARM6)
-  set(CMAKE_C_FLAGS_RELEASE "-O2 -DNDEBUG")
-  set(CMAKE_CXX_FLAGS_RELEASE "-O2 -DNDEBUG")
+  set(OPT_FLAGS_RELEASE "-O2")
 else()
-  set(CMAKE_C_FLAGS_RELEASE "-Ofast -DNDEBUG -Wno-unused-variable")
-  set(CMAKE_CXX_FLAGS_RELEASE "-Ofast -DNDEBUG -Wno-unused-variable")
+  set(OPT_FLAGS_RELEASE "-Ofast")
 endif()
 
+set(CMAKE_C_FLAGS_RELEASE "-DNDEBUG ${OPT_FLAGS_RELEASE}")
+set(CMAKE_CXX_FLAGS_RELEASE "-DNDEBUG ${OPT_FLAGS_RELEASE}")
+
 # set this to 0 if per-block checkpoint needs to be disabled
 set(PER_BLOCK_CHECKPOINT 1)
 
@@ -322,7 +323,7 @@ else()
        set(ARCH_FLAG "-march=${ARCH}")
     endif()
   endif()
-  set(WARNINGS "-Wall -Wextra -Wpointer-arith -Wundef -Wvla -Wwrite-strings -Wno-error=extra -Wno-error=deprecated-declarations -Wno-unused-parameter -Wno-error=unused-variable -Wno-error=undef -Wno-error=uninitialized")
+  set(WARNINGS "-Wall -Wextra -Wpointer-arith -Wundef -Wvla -Wwrite-strings -Wno-error=extra -Wno-error=deprecated-declarations -Wno-unused-parameter -Wno-unused-variable -Wno-error=unused-variable -Wno-error=undef -Wno-error=uninitialized")
   if(NOT MINGW)
     set(WARNINGS_AS_ERRORS_FLAG "-Werror")
   endif()
@@ -383,8 +384,8 @@ else()
 
   if(ARM7)
     message(STATUS "Setting ARM7 C and C++ flags")
-    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -O2 -mfloat-abi=hard")
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -O2 -mfloat-abi=hard")
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -mfloat-abi=hard")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -mfloat-abi=hard")
   endif()
 
   if(APPLE)