sys-cluster/nanos6: fix build error

Signed-off-by: Alessandro Barbieri <lssndrbarbieri@gmail.com>

sys-cluster/nanos6/files/nanos6-2.6-include-string.patch

@@ -0,0 +1,10 @@
+--- a/src/hardware-counters/pqos/PQoSHardwareCounters.cpp
++++ b/src/hardware-counters/pqos/PQoSHardwareCounters.cpp
+@@ -7,6 +7,7 @@
+ #include <algorithm>
+ #include <cassert>
+ #include <sys/utsname.h>
++#include <string>
+ 
+ #include "PQoSHardwareCounters.hpp"
+ #include "PQoSTaskHardwareCounters.hpp"

sys-cluster/nanos6/nanos6-2.6-r3.ebuild

@@ -35,6 +35,7 @@ RDEPEND="
 #	jemalloc? ( dev-libs/jemalloc )
 DEPEND="${RDEPEND}"
 
+PATCHES=( "${FILESDIR}/${P}-include-string.patch" )
 # https://github.com/bsc-pm/nanos6/issues/3
 RESTRICT="test"
 #RESTRICT="!test? ( test )"