[libFuzzer] Properly configure tests for Windows.

[mpividori]

Summary

This configuration is necessary, and is included in all the tests suites, like the one for clang, for the main llvm repository, etc.
We need to execute: config.test_format = lit.formats.ShTest(False)
Otherwise, lit will try to use bash, which generated the problems mentioned in: https://reviews.llvm.org/D29515 , or cmd prompt which generates a lot of problems.

[rnk]

lgtm

Eventually we should do a global cleanup to fold this logic into the TestRunner so we don't have to duplicate this junk in ever lit.cfg.

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

 import lit.formats
 import sys
 
 config.name = "LLVMFuzzer"
 config.test_format = lit.formats.ShTest(True)
 config.suffixes = ['.test']
 config.test_source_root = os.path.dirname(__file__)
 
+# Choose between lit's internal shell pipeline runner and a real shell.  If
+# LIT_USE_INTERNAL_SHELL is in the environment, we use that as an override.
+use_lit_shell = os.environ.get("LIT_USE_INTERNAL_SHELL")
+if use_lit_shell:
+    # 0 is external, "" is default, and everything else is internal.
+    execute_external = (use_lit_shell == "0")
+else:
+    # Otherwise we default to internal on Windows and external elsewhere, as
+    # bash on Windows is usually very slow.
+    execute_external = (not sys.platform in ['win32'])
+
+# testFormat: The test format to use to interpret tests.
+#
+# For now we require '&&' between commands, until they get globally killed and
+# the test runner updated.
+config.test_format = lit.formats.ShTest(execute_external)
+
 # Tweak PATH to include llvm tools dir and current exec dir.
 llvm_tools_dir = getattr(config, 'llvm_tools_dir', None)
 if (not llvm_tools_dir) or (not os.path.exists(llvm_tools_dir)):
   lit_config.fatal("Invalid llvm_tools_dir config attribute: %r" % llvm_tools_dir)
 path = os.path.pathsep.join((llvm_tools_dir, config.test_exec_root,
                              config.environment['PATH']))
 config.environment['PATH'] = path