Increase BB to explore for reachability analysis

We pass mcpu=cortex-a55 for our build, which increases BB to the point
where the LLVM default of 32 is not enough.

I ran a fullmte build and did not see any slowdown.

Bug: 229654778
Change-Id: Ifbd1e5427101b2f2f39c067ba3ea4d5cb4a3ba0d

cc/sanitize.go

@@ -77,7 +77,7 @@ var (
 		"-fno-sanitize-recover=integer,undefined"}
 	hwasanGlobalOptions = []string{"heap_history_size=1023", "stack_history_size=512",
 		"export_memory_stats=0", "max_malloc_fill_size=131072", "malloc_fill_byte=0"}
-	memtagStackCommonFlags = []string{"-march=armv8-a+memtag"}
+	memtagStackCommonFlags = []string{"-march=armv8-a+memtag", "-mllvm", "-dom-tree-reachability-max-bbs-to-explore=128"}
 
 	hostOnlySanitizeFlags   = []string{"-fno-sanitize-recover=all"}
 	deviceOnlySanitizeFlags = []string{"-fsanitize-trap=all", "-ftrap-function=abort"}