[C++] Issue with define ARROW_CXX_COMPILER_FLAGS

### Describe the bug, including details regarding any error messages, version, and platform.

The define `ARROW_CXX_COMPILER_FLAGS` has issues with some forms of flags. For instance our build system automatically generates suppressions like `-D__DATE__=\"redacted\"`. The result is a compiler error in `cpp/src/arrow/util/config.h.cmake`.

While cmake could provide correctly escaped flag strings, it is much easier to use raw strings to solve the issue, e.g.:

```
#define ARROW_CXX_COMPILER_FLAGS R"(@CMAKE_CXX_FLAGS@)"
```

### Component(s)

C++