MDEV-10788 Not able to compile source with -DBUILD_CONFIG=mysql_release -DCMAKE_BUILD_TYPE=Debug

It's too plainful to require <my_config.h> to be included first
for third-party storage engines. And anyway, some source files
might not include <my_config.h> at all, so there is no guarantee
that all parts of the binary will see identical definitions of system
structures (e.g. struct stat).

Define _FILE_OFFSET_BITS on the compiler's command line instead.

CMakeLists.txt

@@ -341,6 +341,9 @@ INCLUDE(configure.cmake)
 
 # Common defines and includes
 ADD_DEFINITIONS(-DHAVE_CONFIG_H)
+IF(_FILE_OFFSET_BITS)
+  ADD_DEFINITIONS(-D_FILE_OFFSET_BITS=${_FILE_OFFSET_BITS})
+ENDIF()
 INCLUDE_DIRECTORIES(${CMAKE_CURRENT_BINARY_DIR}/include)
 
 # Add bundled or system zlib.

config.h.cmake

@@ -484,7 +484,6 @@
 #cmakedefine _LARGE_FILES 1
 #cmakedefine _LARGEFILE_SOURCE 1
 #cmakedefine _LARGEFILE64_SOURCE 1
-#cmakedefine _FILE_OFFSET_BITS @_FILE_OFFSET_BITS@
 
 #cmakedefine TIME_WITH_SYS_TIME 1
 
@@ -647,21 +646,4 @@
 #cmakedefine SIZEOF_TIME_T @SIZEOF_TIME_T@
 #cmakedefine TIME_T_UNSIGNED @TIME_T_UNSIGNED@
 
-/*
-  stat structure (from <sys/stat.h>) is conditionally defined
-  to have different layout and size depending on the defined macros.
-  The correct macro is defined in my_config.h, which means it MUST be
-  included first (or at least before <features.h> - so, practically,
-  before including any system headers).
-
-  Check the include order by looking at __GLIBC__ (defined in <features.h>)
-
-  But we cannot force all third-party clients/connectors to include
-  my_config.h first. So, their crashes are their responsibility,
-  we enable this check only for MariaDB sources (SAFE_MUTEX check).
-*/
-#if defined(__GLIBC__) && defined(SAFE_MUTEX)
-#error <my_config.h> MUST be included first!
-#endif
-
 #endif