mariadb: blacklist builds for i686

Due to error:

In file included from /home/builder/.termux-build/mariadb/src/mysys/my_new.cc:25:
In file included from /home/builder/.termux-build/mariadb/src/mysys/mysys_priv.h:20:
In file included from /home/builder/.termux-build/mariadb/src/include/my_sys.h:34:
/home/builder/.termux-build/mariadb/src/include/my_pthread.h:822:10: error: use of undeclared identifier 'my_atomic_add32'
  (void) my_atomic_add32_explicit(value, 1, MY_MEMORY_ORDER_RELAXED);

packages/mariadb/build.sh

@@ -11,6 +11,11 @@ TERMUX_PKG_BREAKS="mariadb-dev"
 TERMUX_PKG_REPLACES="mariadb-dev"
 TERMUX_PKG_SERVICE_SCRIPT=("mysqld" 'exec mysqld --basedir=$PREFIX --datadir=$PREFIX/var/lib/mysql 2>&1')
 
+# i686 build fails due to:
+#  /home/builder/.termux-build/mariadb/src/include/my_pthread.h:822:10: error: use of undeclared identifier 'my_atomic_add32'
+#    (void) my_atomic_add32_explicit(value, 1, MY_MEMORY_ORDER_RELAXED);
+TERMUX_PKG_BLACKLISTED_ARCHES="i686"
+
 TERMUX_PKG_EXTRA_CONFIGURE_ARGS="
 -DBISON_EXECUTABLE=$(which bison)
 -DGETCONF=$(which getconf)