[libc] Disable testing for NVPTX debug builds (#86856)

Summary:
Debug builds don't optimize out certain parts of the code that end up
making the GPU backend crash. This results in regular builds not being
successful just to build the testing objects. Disable them for now in
debug mode.
GitOrigin-RevId: daa755ba7b7fe11e078f1e6f43d446234023f859
1 file changed