Address a bunch of clang-tidy complaints.

There were a bunch more unreasonable/incorrect ones, but these ones
seemed legit. Nothing very interesting, though.

Bug: N/A
Test: ran tests, benchmarks
Change-Id: If66971194d4a7b4bf6d0251bedb88e8cdc88a76f
diff --git a/libc/malloc_debug/OptionData.h b/libc/malloc_debug/OptionData.h
index 80190f5..5c2d272 100644
--- a/libc/malloc_debug/OptionData.h
+++ b/libc/malloc_debug/OptionData.h
@@ -34,7 +34,7 @@
 
 class OptionData {
  public:
-  OptionData(DebugData* debug) : debug_(debug) {}
+  explicit OptionData(DebugData* debug) : debug_(debug) {}
   ~OptionData() = default;
 
  protected: