[fuzzer,CMake] Group fuzzer lit test into one check-fuzzer

For now check-fuzzer is just a cmake target that depends
on different check-fuzzer-xxx lit test targets. This causes
check-fuzzer get seperate lit test results like this:

```
********************
********************
Failed Tests (1):
  libFuzzer :: fuzzer-flags.test

Testing Time: 19.80s
  Unsupported      :   7
  Passed           : 128
  Expectedly Failed:   3
  Failed           :   1
make[3]: *** [projects/compiler-rt/test/fuzzer/CMakeFiles/check-fuzzer-default-x86_64.dir/build.make:71: projects/compiler-rt/test/fuzzer/CMakeFiles/check-fuzzer-default-x86_64] Error 1
make[2]: *** [CMakeFiles/Makefile2:36745: projects/compiler-rt/test/fuzzer/CMakeFiles/check-fuzzer-default-x86_64.dir/all] Error 2
make[2]: *** Waiting for unfinished jobs....
--

********************
********************
Failed Tests (1):
  libFuzzer :: fuzzer-flags.test

Testing Time: 24.33s
  Unsupported:  21
  Passed     : 117
  Failed     :   1
make[3]: *** [projects/compiler-...