[clang][test] Use a physical copy of FS

Make use of a physical copy, rather than real FS in unittests that
change working-directory to get rid of the side effect of changing cwd for the
whole process. It's triggering crashes depending on the test order.

Differential Revision: https://reviews.llvm.org/D152265

Author: kadircet

clang/unittests/Serialization/ModuleCacheTest.cpp

@@ -14,6 +14,7 @@
 #include "clang/Lex/HeaderSearch.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/Support/FileSystem.h"
+#include "llvm/Support/VirtualFileSystem.h"
 #include "llvm/Support/raw_ostream.h"
 
 #include "gtest/gtest.h"
@@ -98,6 +99,7 @@ TEST_F(ModuleCacheTest, CachedModuleNewPath) {
       CompilerInstance::createDiagnostics(new DiagnosticOptions());
   CreateInvocationOptions CIOpts;
   CIOpts.Diags = Diags;
+  CIOpts.VFS = llvm::vfs::createPhysicalFileSystem();
 
   // First run should pass with no errors
   const char *Args[] = {"clang",        "-fmodules",          "-Fframeworks",

clang/unittests/Serialization/NoCommentsTest.cpp

@@ -87,6 +87,7 @@ void foo() {}
       CompilerInstance::createDiagnostics(new DiagnosticOptions());
   CreateInvocationOptions CIOpts;
   CIOpts.Diags = Diags;
+  CIOpts.VFS = llvm::vfs::createPhysicalFileSystem();
 
   std::string CacheBMIPath = llvm::Twine(TestDir + "/Comments.pcm").str();
   const char *Args[] = {

clang/unittests/Serialization/VarDeclConstantInitTest.cpp

@@ -94,6 +94,7 @@ export namespace Fibonacci
       CompilerInstance::createDiagnostics(new DiagnosticOptions());
   CreateInvocationOptions CIOpts;
   CIOpts.Diags = Diags;
+  CIOpts.VFS = llvm::vfs::createPhysicalFileSystem();
 
   std::string CacheBMIPath = llvm::Twine(TestDir + "/Cached.pcm").str();
   const char *Args[] = {