[libFuzzer] Add features `windows` and `posix` for lit tests.

[mpividori]

Summary

I add 2 features: posix and windows.
Sometimes we want some specific tests only for posix and we use:

REQUIRES: posix

Sometimes we want some specific tests only for windows and we use:

REQUIRES: windows

[kcc]

LGTM

llvm/trunk/lib/Fuzzer/test/CMakeLists.txt

 set(TestBinaries ${TestBinaries} LLVMFuzzer-DSOTest)
 
 ###############################################################################
 # Configure lit to run the tests
 #
 # Note this is done after declaring all tests so we can inform lit if any tests
 # need to be disabled.
 ###############################################################################
+set(LIBFUZZER_POSIX 1)
+if (MSVC)
+  set(LIBFUZZER_POSIX 0)
+endif()
 
 configure_lit_site_cfg(
   ${CMAKE_CURRENT_SOURCE_DIR}/lit.site.cfg.in
   ${CMAKE_CURRENT_BINARY_DIR}/lit.site.cfg
   )
 
 configure_lit_site_cfg(
   ${CMAKE_CURRENT_SOURCE_DIR}/unit/lit.site.cfg.in

llvm/trunk/lib/Fuzzer/test/lit.cfg

 config.environment['PATH'] = path
 
 if config.has_lsan:
   lit_config.note('lsan feature available')
   config.available_features.add('lsan')
 else:
   lit_config.note('lsan feature unavailable')
 
+if sys.platform.startswith('win') or sys.platform.startswith('cygwin'):
+  config.available_features.add('windows')
+
+if config.is_posix:
+  config.available_features.add('posix')
+
 if sys.platform.startswith('linux'):
   # Note the value of ``sys.platform`` is not consistent
   # between python 2 and 3, hence the use of ``.startswith()``.
   lit_config.note('linux feature available')
   config.available_features.add('linux')
 else:
   lit_config.note('linux feature unavailable')

llvm/trunk/lib/Fuzzer/test/lit.site.cfg.in

 config.test_exec_root = "@CMAKE_CURRENT_BINARY_DIR@"
 config.llvm_tools_dir = "@LLVM_TOOLS_DIR@"
 config.has_lsan = True if @HAS_LSAN@ == 1 else False
+config.is_posix = @LIBFUZZER_POSIX@
 lit_config.load_config(config, "@CMAKE_CURRENT_SOURCE_DIR@/lit.cfg")