While displaying line numbers, show the relevant line number inside
the recipe not just the first line of the entire recipe.
Sample changes suggested by Brian Vandenberg <phantall@gmail.com>
* gnumake.h (gmk_floc): Add an 'offset' to track the recipe offset.
* read.c (eval, eval_makefile, eval_buffer): Initialize 'offset'.
(record_files, install_pattern_rule): Ditto.
* job.c (new_job, job_next_command): Update 'offset' based on the
line of the recipe we're expanding or invoking.
(child_error): Add 'offset' when showing the line number.
* function.c (func_shell_base): Ditto.
* output.c (error, fatal): Ditto.
* NEWS: Mention the new ability.
* tests/scripts/features/errors: Check the line number on errors.
* tests/scripts/functions/warning: Check the line number on warnings.
* tests/scripts/features/output-sync,
tests/scripts/features/parallelism, tests/scripts/functions/shell,
tests/scripts/functions/error: Update line numbers.
