'make check-performance' from libstdc++-v3?

[Benjamin Kosnik]

>a curiosity: why, having build the library, 'make check-performance'
>only works from libstdc++-v3/testsuite, whereas 'make check' works
>fine from the libstdc++-v3 directory itself?

I was trying to keep all the extra check targets in the
testsuite/Makefile.am file. I think this makes sense, as it localizes
the testsuite bits in the correct place.

Perhaps I was wrong.

-benjamin