Optimized VmaCountBitsSets to use std::popcount when C++20 is enabled

Closes #251

include/vk_mem_alloc.h

diff --git a/include/vk_mem_alloc.h b/include/vk_mem_alloc.h
index 256b654..98aa40f 100644
--- a/include/vk_mem_alloc.h
+++ b/include/vk_mem_alloc.h
@@ -2574,6 +2574,9 @@
 #ifdef _MSC_VER

     #include <intrin.h> // For functions like __popcnt, _BitScanForward etc.

 #endif

+#if __cplusplus >= 202002L || _MSVC_LANG >= 202002L // C++20

+    #include <bit> // For std::popcount

+#endif

 

 /*******************************************************************************

 CONFIGURATION SECTION

@@ -3176,12 +3179,16 @@
 */

 static inline uint32_t VmaCountBitsSet(uint32_t v)

 {

+#if __cplusplus >= 202002L || _MSVC_LANG >= 202002L // C++20

+    return std::popcount(v);

+#else

     uint32_t c = v - ((v >> 1) & 0x55555555);

     c = ((c >> 2) & 0x33333333) + (c & 0x33333333);

     c = ((c >> 4) + c) & 0x0F0F0F0F;

     c = ((c >> 8) + c) & 0x00FF00FF;

     c = ((c >> 16) + c) & 0x0000FFFF;

     return c;

+#endif

 }

 

 static inline uint8_t VmaBitScanLSB(uint64_t mask)