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/RecordData.h b/libc/malloc_debug/RecordData.h
index 6e19923..ccabac2 100644
--- a/libc/malloc_debug/RecordData.h
+++ b/libc/malloc_debug/RecordData.h
@@ -66,7 +66,7 @@
 
 class AllocEntry : public RecordEntry {
  public:
-  AllocEntry(void* pointer);
+  explicit AllocEntry(void* pointer);
   virtual ~AllocEntry() = default;
 
  protected:
@@ -92,7 +92,7 @@
 
 class FreeEntry : public AllocEntry {
  public:
-  FreeEntry(void* pointer);
+  explicit FreeEntry(void* pointer);
   virtual ~FreeEntry() = default;
 
   std::string GetString() const override;