common/swap: Mark byte swapping free functions with [[nodiscard]] and noexcept

Allows the compiler to inform when the result of a swap function is
being ignored (which is 100% a bug in all usage scenarios). We also mark
them noexcept to allow other functions using them to be able to be
marked as noexcept and play nicely with things that potentially inspect
"nothrowability".

src/common/swap.h

@@ -57,13 +57,13 @@
 namespace Common {
 
 #ifdef _MSC_VER
-inline u16 swap16(u16 data) {
+[[nodiscard]] inline u16 swap16(u16 data) noexcept {
     return _byteswap_ushort(data);
 }
-inline u32 swap32(u32 data) {
+[[nodiscard]] inline u32 swap32(u32 data) noexcept {
     return _byteswap_ulong(data);
 }
-inline u64 swap64(u64 data) {
+[[nodiscard]] inline u64 swap64(u64 data) noexcept {
     return _byteswap_uint64(data);
 }
 #elif defined(__clang__) || defined(__GNUC__)
@@ -73,29 +73,29 @@ inline u64 swap64(u64 data) {
 #undef swap32
 #undef swap64
 #endif
-inline u16 swap16(u16 data) {
+[[nodiscard]] inline u16 swap16(u16 data) noexcept {
     return __builtin_bswap16(data);
 }
-inline u32 swap32(u32 data) {
+[[nodiscard]] inline u32 swap32(u32 data) noexcept {
     return __builtin_bswap32(data);
 }
-inline u64 swap64(u64 data) {
+[[nodiscard]] inline u64 swap64(u64 data) noexcept {
     return __builtin_bswap64(data);
 }
 #else
 // Slow generic implementation.
-inline u16 swap16(u16 data) {
+[[nodiscard]] inline u16 swap16(u16 data) noexcept {
     return (data >> 8) | (data << 8);
 }
-inline u32 swap32(u32 data) {
+[[nodiscard]] inline u32 swap32(u32 data) noexcept {
     return (swap16(data) << 16) | swap16(data >> 16);
 }
-inline u64 swap64(u64 data) {
+[[nodiscard]] inline u64 swap64(u64 data) noexcept {
     return ((u64)swap32(data) << 32) | swap32(data >> 32);
 }
 #endif
 
-inline float swapf(float f) {
+[[nodiscard]] inline float swapf(float f) noexcept {
     static_assert(sizeof(u32) == sizeof(float), "float must be the same size as uint32_t.");
 
     u32 value;
@@ -107,7 +107,7 @@ inline float swapf(float f) {
     return f;
 }
 
-inline double swapd(double f) {
+[[nodiscard]] inline double swapd(double f) noexcept {
     static_assert(sizeof(u64) == sizeof(double), "double must be the same size as uint64_t.");
 
     u64 value;