[clang][deps] Call getMemBuffer with RequiresNullTerminator false (#195072)

The getMemBuffer() has a default parameter RequiresNullTerminator which
is set to true.

In ModuleCache the MemoryBuffer::getOpenFile is called with /*
RequiresNullTerminator=*/false. This means that initial contents of the
MemoryBuffer may not have a trailing 0x0 at the end of the file.

When assertions are enabled and RequiresNullTerminator is true the
MemoryBuffer will trigger a "Buffer is not null terminated!" assertion
failure if BufEnd[0] != 0.

We have at one build with assertions enabled that is triggering this
MemoryBuffer assertion failure in the check-clang tests:
* ClangScanDeps/modules-dep-args.c
* Driver/modules-driver-import-std.cpp

The failure is specific to one particular machine, we have not been able
to reproduce locally. It is possible that the failure is filesystem type
or path length dependent.

Changing the RequiresNullTerminator in getMemBuffer to false to match
the value of RequiresNullTerminator in getOpenFile fixes the problem and
all tests pass.

clang/lib/DependencyScanning/InProcessModuleCache.cpp

@@ -179,7 +179,8 @@ public:
     }
     Size = Entry.Buffer->getBufferSize();
     ModTime = Entry.ModTime;
-    return llvm::MemoryBuffer::getMemBuffer(*Entry.Buffer);
+    return llvm::MemoryBuffer::getMemBuffer(*Entry.Buffer,
+                                            /* RequiresNullTerminator */ false);
   }
 };
 } // namespace