sanitizer_allocator.cpp: Ensure at least sizeof(void*) alignment

Some platforms (e.g. 64-bit CHERI) have stronger alignment requirements
on values returned from allocators. For all other platforms this does
not result in any functional change.

Reviewed By: cjappl, vitalybuka

Pull Request: #84440

Author: arichardson

compiler-rt/lib/sanitizer_common/sanitizer_allocator.cpp

@@ -59,7 +59,7 @@ static void *RawInternalAlloc(uptr size, InternalAllocatorCache *cache,
 
 static void *RawInternalRealloc(void *ptr, uptr size,
                                 InternalAllocatorCache *cache) {
-  uptr alignment = 8;
+  constexpr usize alignment = Max<usize>(8, sizeof(void *));
   if (cache == 0) {
     SpinMutexLock l(&internal_allocator_cache_mu);
     return internal_allocator()->Reallocate(&internal_allocator_cache, ptr,
@@ -137,7 +137,8 @@ void InternalAllocatorUnlock() SANITIZER_NO_THREAD_SAFETY_ANALYSIS {
 }
 
 // LowLevelAllocator
-constexpr uptr kLowLevelAllocatorDefaultAlignment = 8;
+constexpr usize kLowLevelAllocatorDefaultAlignment =
+    Max<usize>(8, sizeof(void *));
 constexpr uptr kMinNumPagesRounded = 16;
 constexpr uptr kMinRoundedSize = 65536;
 static uptr low_level_alloc_min_alignment = kLowLevelAllocatorDefaultAlignment;