crypto/mem.c: switch to tsan_assist.h in CRYPTO_MDEBUG.

Rationale is that it wasn't providing accurate statistics anyway.
For statistics to be accurate CRYPTO_get_alloc_counts should acquire
a lock and lock-free additions should not be an option.
Reviewed-by: NPaul Dale <paul.dale@oracle.com>
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6786)

crypto/mem.c

@@ -31,13 +31,13 @@ static void (*free_impl)(void *, const char *, int)
     = CRYPTO_free;
 
 #ifndef OPENSSL_NO_CRYPTO_MDEBUG
-static int malloc_count;
-static int realloc_count;
-static int free_count;
-static int dummy;
+# include "internal/tsan_assist.h"
 
-# define INCREMENT(x) CRYPTO_atomic_add(&x, 1, &dummy, memdbg_lock)
-# define GET(ret, val) CRYPTO_atomic_read(&val, ret, memdbg_lock)
+static TSAN_QUALIFIER int malloc_count;
+static TSAN_QUALIFIER int realloc_count;
+static TSAN_QUALIFIER int free_count;
+
+# define INCREMENT(x) tsan_counter(&(x))
 
 static char *md_failstring;
 static long md_count;
@@ -98,11 +98,11 @@ void CRYPTO_get_mem_functions(
 void CRYPTO_get_alloc_counts(int *mcount, int *rcount, int *fcount)
 {
     if (mcount != NULL)
-        GET(mcount, malloc_count);
+        *mcount = tsan_load(&malloc_count);
     if (rcount != NULL)
-        GET(rcount, realloc_count);
+        *rcount = tsan_load(&realloc_count);
     if (fcount != NULL)
-        GET(fcount, free_count);
+        *fcount = tsan_load(&free_count);
 }
 
 /*