[BUG] configure fails to find std::hash when the clang compiler is used

[Yuri Vic]

| int

| main ()

| {

| if (sizeof ((std::hash<int>)))

|           return 0;

|   ;

|   return 0;

| }

configure:6069: result: yes

configure:6083: checking for std::tr1::hash<int>

configure:6083: c++ -c -O2 -pipe -fno-omit-frame-pointer -fstack-protector -isystem /usr/local/include -fno-strict-aliasing -fno-omit-frame-pointer  -isystem /usr/local/include  -fno-omit-frame-pointer -isystem /usr/local/include conftest.cpp >&5

conftest.cpp:39:18: error: no member named 'tr1' in namespace 'std'

if (sizeof (std::tr1::hash<int>))

            ~~~~~^

conftest.cpp:39:31: error: expected '(' for function-style cast or type construction

if (sizeof (std::tr1::hash<int>))

                           ~~~^

conftest.cpp:39:32: error: expected expression

if (sizeof (std::tr1::hash<int>))

                               ^