Link with libatomic to enable C11 atomics support

Some architectures (mips) require libatomic to support proper
atomic operations. Check first if support is available without
linking, otherwise use the library.

Contributors:
James Cowgill <jcowgill@debian.org>
Jessica Clarke <jrtc27@debian.org>
Vicențiu Ciorbaru <vicentiu@mariadb.org>

configure.cmake

@@ -895,7 +895,25 @@ int main()
   long long int *ptr= &var;
   return (int)__atomic_load_n(ptr, __ATOMIC_SEQ_CST);
 }"
-HAVE_GCC_C11_ATOMICS)
+HAVE_GCC_C11_ATOMICS_WITHOUT_LIBATOMIC)
+IF (HAVE_GCC_C11_ATOMICS_WITHOUT_LIBATOMIC)
+  SET(HAVE_GCC_C11_ATOMICS True)
+ELSE()
+  SET(OLD_CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES})
+  LIST(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
+  CHECK_CXX_SOURCE_COMPILES("
+  int main()
+  {
+    long long int var= 1;
+    long long int *ptr= &var;
+    return (int)__atomic_load_n(ptr, __ATOMIC_SEQ_CST);
+  }"
+  HAVE_GCC_C11_ATOMICS_WITH_LIBATOMIC)
+  IF(HAVE_GCC_C11_ATOMICS_WITH_LIBATOMIC)
+    SET(HAVE_GCC_C11_ATOMICS True)
+  ENDIF()
+  SET(CMAKE_REQUIRED_LIBRARIES ${OLD_CMAKE_REQUIRED_LIBRARIES})
+ENDIF()
 
 IF(WITH_VALGRIND)
   SET(HAVE_valgrind 1)

mysys/CMakeLists.txt

@@ -78,6 +78,10 @@ TARGET_LINK_LIBRARIES(mysys dbug strings ${ZLIB_LIBRARY}
  ${LIBNSL} ${LIBM} ${LIBRT} ${CMAKE_DL_LIBS} ${LIBSOCKET} ${LIBEXECINFO} ${CRC32_LIBRARY})
 DTRACE_INSTRUMENT(mysys)
 
+IF (HAVE_GCC_C11_ATOMICS_WITH_LIBATOMIC)
+  TARGET_LINK_LIBRARIES(mysys atomic)
+ENDIF()
+
 IF(HAVE_BFD_H)
   TARGET_LINK_LIBRARIES(mysys bfd)  
 ENDIF(HAVE_BFD_H)

sql/CMakeLists.txt

@@ -307,7 +307,6 @@ IF(WITH_MYSQLD_LDFLAGS)
      "${MYSQLD_LINK_FLAGS} ${WITH_MYSQLD_LDFLAGS}")
 ENDIF()
 
-
 FIND_PACKAGE(BISON 2.0)