mysql: change wrong #include <sys/poll.h>

This avoids lots of warnings when compiling packages
with dependency mysql-devel for musl libc.

srcpkgs/mysql/template

@@ -1,7 +1,7 @@
 # Template file for 'mysql'
 pkgname=mysql
 version=5.6.27
-revision=1
+revision=2
 build_style=cmake
 configure_args="-DSYSCONFDIR=/etc/mysql -DMYSQL_DATADIR=/var/lib/mysql
  -DMYSQL_UNIX_ADDR=/run/mysqld/mysqld.sock -DDEFAULT_CHARSET=utf8
@@ -38,6 +38,7 @@ CFLAGS="-D__STDC_ISO_10646__"
 pre_configure() {
 	# libressl major detection.
 	sed -i '/OPENSSL_MAJOR_VERSION/s/1/2/' cmake/ssl.cmake
+	sed -i 's/sys\/poll\.h/poll.h/' include/my_net.h
 
 	# We need some host binaries before starting cross compilation.
 	if [ "$CROSS_BUILD" ]; then