|    Unfortunately, this does not use the installed compiler.  Sigh.
   |    So you need to stick the testsuite tree on the end of
   |    src/gnu/dist/toolchain/gcc/ and use that instead.
   |
   | it's easy to do "install-tree" testing.  just set CC, etc.
   | and run make check as usual.
   
   When I tried setting CC it was ignored.  I think the testsuite
   is hard-wired to use .../gcc/xgcc for tests.


ah, try GCC_UNDER_TEST.