[compiler-rt][lsan][Fuchsia] Adjust lsan allocator settings (#69401)

These now match the settings for the asan allocator on Fuchsia+RISCV.

Author: PiJoules

compiler-rt/lib/lsan/lsan_allocator.h

@@ -68,8 +68,23 @@ using PrimaryAllocator = PrimaryAllocatorASVT<LocalAddressSpaceView>;
 #else
 # if SANITIZER_FUCHSIA || defined(__powerpc64__)
 const uptr kAllocatorSpace = ~(uptr)0;
+#    if SANITIZER_RISCV64
+// See the comments in compiler-rt/lib/asan/asan_allocator.h for why these
+// values were chosen.
+const uptr kAllocatorSize = UINT64_C(1) << 33;  // 8GB
+using LSanSizeClassMap = SizeClassMap</*kNumBits=*/2,
+                                      /*kMinSizeLog=*/5,
+                                      /*kMidSizeLog=*/8,
+                                      /*kMaxSizeLog=*/18,
+                                      /*kNumCachedHintT=*/8,
+                                      /*kMaxBytesCachedLog=*/10>;
+static_assert(LSanSizeClassMap::kNumClassesRounded <= 32,
+              "32 size classes is the optimal number to ensure tests run "
+              "effieciently on Fuchsia.");
+#    else
 const uptr kAllocatorSize  =  0x40000000000ULL;  // 4T.
 using LSanSizeClassMap = DefaultSizeClassMap;
+#    endif
 #  elif SANITIZER_RISCV64
 const uptr kAllocatorSpace = ~(uptr)0;
 const uptr kAllocatorSize = 0x2000000000ULL;  // 128G.