Fix compile error - linker does not find extern variables, in sql_logger.c

The file uses external variables defined in another (C++) source file. Since MSVC mangles variables and not only functions, either variables in question should be extern "C", or  sql_logger should be made C++ for link to succeed.

Fixed by renaming sql_logger.c to sql_logger.cc

libmysqld/CMakeLists.txt

@@ -95,7 +95,7 @@ SET(SQL_EMBEDDED_SOURCES emb_qcache.cc libmysqld.c lib_sql.cc
            ../sql/create_options.cc ../sql/rpl_utility.cc
            ../sql/rpl_reporting.cc
            ../sql/sql_expression_cache.cc
-           ../sql/sql_logger.c
+           ../sql/sql_logger.cc
            ${GEN_SOURCES}
            ${MYSYS_LIBWRAP_SOURCE}
 )

sql/CMakeLists.txt

@@ -85,7 +85,7 @@ SET (SQL_SOURCE
                gcalc_slicescan.cc gcalc_tools.cc
 			   threadpool_common.cc 
 			   ../sql-common/mysql_async.c
-                           sql_logger.c
+                           sql_logger.cc
                ${GEN_SOURCES}
                ${MYSYS_LIBWRAP_SOURCE}
 			   )