Fix incorrect flag handling and string escaping in the `make host_info`
diagnostic target.
Previously, CFLAGS, CXXFLAGS, and LDFLAGS were passed in a form that caused
improper splitting and quoting, which resulted in malformed output and
incorrectly escaped configuration values such as CONFIG_APPS_DIR.
This change ensures that:
- Compilation flags are passed as proper shell strings
- Flags are split correctly using shlex
- Configuration values are escaped exactly once when generating sysinfo.h
- Parsed output matches the contents of the .config file
This change affects diagnostic output only and does not modify the NuttX
build process or generated binaries.
Signed-off-by: Adwait Godbole <adwaitngodbole@gmail.com>