emulators/rpcs3: unbreak on FreeBSD < 12.2 after r533715

In file included from rpcs3/Emu/System.cpp:1:
In file included from rpcs3/stdafx.h:25:
rpcs3/util/atomic.hpp:370:47: error: invalid output constraint '=@ccc' in asm

__asm__("lock btsw %2, %0\n" : "+m" (dest), "=@ccc" (result) : "Ir" (_bit) : "cc");
                                            ^

rpcs3/util/atomic.hpp:378:46: error: invalid output constraint '=@ccc' in asm

__asm__("lock btrw %2, %0\n": "+m" (dest), "=@ccc" (result) : "Ir" (_bit) : "cc");
                                           ^

rpcs3/util/atomic.hpp:386:46: error: invalid output constraint '=@ccc' in asm

__asm__("lock btcw %2, %0\n": "+m" (dest), "=@ccc" (result) : "Ir" (_bit) : "cc");
                                           ^

rpcs3/util/atomic.hpp:491:47: error: invalid output constraint '=@ccc' in asm

__asm__("lock btsl %2, %0\n" : "+m" (dest), "=@ccc" (result) : "Ir" (bit) : "cc");
                                            ^

rpcs3/util/atomic.hpp:498:47: error: invalid output constraint '=@ccc' in asm

__asm__("lock btrl %2, %0\n" : "+m" (dest), "=@ccc" (result) : "Ir" (bit) : "cc");
                                            ^

rpcs3/util/atomic.hpp:505:47: error: invalid output constraint '=@ccc' in asm

__asm__("lock btcl %2, %0\n" : "+m" (dest), "=@ccc" (result) : "Ir" (bit) : "cc");
                                            ^

rpcs3/util/atomic.hpp:611:47: error: invalid output constraint '=@ccc' in asm

__asm__("lock btsq %2, %0\n" : "+m" (dest), "=@ccc" (result) : "Ir" (_bit) : "cc");
                                            ^

rpcs3/util/atomic.hpp:619:47: error: invalid output constraint '=@ccc' in asm

__asm__("lock btrq %2, %0\n" : "+m" (dest), "=@ccc" (result) : "Ir" (_bit) : "cc");
                                            ^

rpcs3/util/atomic.hpp:627:47: error: invalid output constraint '=@ccc' in asm

__asm__("lock btcq %2, %0\n" : "+m" (dest), "=@ccc" (result) : "Ir" (_bit) : "cc");
                                            ^

In file included from rpcs3/Emu/System.cpp:22:
In file included from rpcs3/Emu/RSX/GSRender.h:3:
In file included from rpcs3/Emu/RSX/RSXThread.h:10:
In file included from rpcs3/Emu/RSX/rsx_cache.h:11:
In file included from rpcs3/Emu/RSX/Common/texture_cache_checker.h:3:
rpcs3/Emu/RSX/Common/../rsx_utils.h:895:22: error: comparison of integers of different signs: 'int' and 'u32' (aka 'unsigned int') [-Werror,-Wsign-compare]

for (int n = 0; n < initial_size; ++n)
                ~ ^ ~~~~~~~~~~~~