[Memprof] Changes HISTOGRAM_GRANULARITY from 8U to 8ULL. (llvm#100949)

This changes a bug in memprofiling with histogram where the shadow mask
would be `0xFFFFFFF8` instead of `0xFFFFFFFFFFFFFFF8`, essentially
discarding the upper 32 bits of the address. This can cause different
addresses to be mapped to the same shadow address.

compiler-rt/lib/memprof/memprof_mapping.h

@@ -55,7 +55,7 @@ extern uptr kHighMemEnd; // Initialized in __memprof_init.
 // computed by summing up all individual 1 byte counters. This can incur an
 // accuracy penalty.
 
-#define HISTOGRAM_GRANULARITY 8U
+#define HISTOGRAM_GRANULARITY 8ULL
 
 #define HISTOGRAM_MAX_COUNTER 255U