libgo/testsuite: add benchmarks and examples to list

In CL 384695 I simplified the code that built lists of benchmarks,
examples, and fuzz tests, and managed to break it. This CL corrects
the code to once again make the benchmarks available, and to run
the examples with output and the fuzz targets.

Doing this revealed a test failure in internal/fuzz on 32-bit x86:
a signalling NaN is turned into a quiet NaN on the 387 floating-point
stack that GCC uses by default. This CL skips the test.

Fixes golang/go#60826

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/503798