[libFuzzer] [NFC] Split fuzzer.test into smaller tests

Keeping fuzzer.test together as a gigantic test has no advantages and multiple disadvantages:

 - Worse test parallelization (fuzzer.test is always blocking the test
run on a machine with many cores)
 - Debugging test failures is made more difficult (not clear what fails
from fuzzer.test failing)
 - Makes porting tests to new platforms more difficult (whenever
fuzzer.test fails have to inspect the output to figure out what is going
on, and then restart all of it)
 - Hides dead code (in our case, "Done1000000" FileCheck variable was
never used, DISABLED: not %t-UninstrumentedTest-Uninstrumented was never
compiled, and there was small amount of duplication vs. simple-cmp.test)
 - Makes correspondence between LIT .test files and .cpp files less
straightforward

Differential Revision: https://reviews.llvm.org/D46557

llvm-svn: 332145