sim: common: add $LINENO rewriting support to genmloop scripts

sim: common: add $LINENO rewriting support to genmloop scripts

The generated mloop files can trigger compile time warnings.  It can
be difficult to see/understand where the original code is coming from
as all the diagnostics point to the generated output.  Using #line
pragmas, we can point people to the original source files.

Unfortunately, this code is written in POSIX shell, and that lacks
support for line number tracking.  The $LINENO variable, even when
available, can just be plain wrong.  For example, when using dash
and subshells, $LINENO can end up having negative values.  Add a
wrapper script that will uses awk to rewrite the $LINENO variable
to the right value to avoid all that.

Basically lineno.sh takes an input script, rewrites all uses of
$LINENO into the actual line number (and $0 into the original file
name), and then executes the temporary script.

This commit doesn't actually add #line pragmas to any files.  That
comes next.