Default: -g enables line/column debug info

[krystophny]

Summary

• Make -g automatically enable --debug-with-line-column so debug builds always include line/column location info.
• Prevents “emit_debug_line_column is not enabled” errors when users or CMake add -g implicitly.

Test plan

• src/bin/lfortran -g -c integration_tests/print_01.f90 (no extra flags; succeeds).
• cmake --build lfortran/build (updates binaries with the new default).

[krystophny]

Does this make more sense than throwing an error and requiring another CLI flag? I ran into this often when running with cmake Debug settings.

[certik]

This PR makes emit_debug_line_column useless, as it is always on together with -g, so just remove it completely. We'll only use -g and if enabled, the linear index always gets converted to line/column. It's slower, but -g is already slower and we can implement the linear index later --- the idea was that we would only convert the linear index to line/column in our runtime to print a stacktrace. But using the default debug info requires line/column, so let's just use it by default.

[krystophny]

This PR makes emit_debug_line_column useless, as it is always on together with -g, so just remove it completely. We'll only use -g and if enabled, the linear index always gets converted to line/column. It's slower, but -g is already slower and we can implement the linear index later --- the idea was that we would only convert the linear index to line/column in our runtime to print a stacktrace. But using the default debug info requires line/column, so let's just use it by default.

Done!