Can testcrate/build.rs and some other redundant things be deleted?

[AaronKutch]

After PR #384 was merged, I thought I would look around and try to close as many easy issues as I could while my brain is still familiar with compiler-builtins. I realized that issues #162 and #168 was caused by the fact that fixing the exponent would enable the generation of subnormal numbers, and the soft multiplication does not support subnormal numbers (at least not yet). I haven't messed with build.rs much because I thought it was doing some really special testing. After looking it over, I realize all it is is a hackier version of the tests now under tests/. It doesn't go anywhere near the level of rigorousness my new tests achieve (it hasn't found any of the subnormal or rounding edge cases #384 found).

The only thing build.rs has that the new testing suite doesn't is a few more tests related to the special intrinsics that ARM gets. Should I open a PR to test the remaining functions and delete build.rs and tests/generated.rs altogether? Also, I think the references to panic-handler and utest_macros crates can be deleted. Some documentation says they were introduced as a workaround for rust-lang/rust#51647, but that issue was closed a long time ago.

[alexcrichton]

I think as long as we test basically the same amount of things it's fine to refactor/clean up as necessary personally. I forget the exact intricacies of how this is all tested, but I see no reason to keep one specific way of testing over another!

[AaronKutch]

fixed by #397