MDEV-18417/MDEV-18656/MDEV-18417: Work around compiler ASAN bug

In a Ubuntu Xenial build environment, the compiler identified as
g++-5.real (Ubuntu 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609
seems to be emitting incorrect code for the compilation unit
trx0rec.cc, triggering a bogus-looking AddressSanitizer report
of an invalid read of something in the function trx_undo_rec_get_pars().
This is potentially affecting any larger tests where the InnoDB
purge subsystem is being exercised.

When the optimization level of trx0rec.cc is limited to -O1, no
bogus failure is being reported. With -O2 or -O3, a lot of things
seemed to be inlined in the function, and the disassembly of the
generated code did not make sense to me.

storage/innobase/CMakeLists.txt

@@ -1,4 +1,5 @@
 # Copyright (c) 2006, 2017, Oracle and/or its affiliates. All rights reserved.
+# Copyright (c) 2019, MariaDB Corporation.
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -74,6 +75,12 @@ SET(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -DUNIV_DEBUG -DUNIV_SYNC_DEB
 CHECK_FUNCTION_EXISTS(sched_getcpu  HAVE_SCHED_GETCPU)
 
 IF(NOT MSVC)
+  # Work around MDEV-18417, MDEV-18656, MDEV-18417
+  IF(WITH_ASAN AND CMAKE_COMPILER_IS_GNUCC AND
+     CMAKE_C_COMPILER_VERSION VERSION_LESS "6.0.0")
+    SET_SOURCE_FILES_PROPERTIES(trx/trx0rec.cc PROPERTIES COMPILE_FLAGS -O1)
+  ENDIF()
+
   # either define HAVE_IB_GCC_ATOMIC_BUILTINS or not
   # workaround for old gcc on x86, gcc atomic ops only work under -march=i686
   IF(CMAKE_SYSTEM_PROCESSOR STREQUAL "i686" AND CMAKE_COMPILER_IS_GNUCC AND