rename --verbose to --verbose-spawn and limit the scope of what it does

[andrewrk]

Extracted from #14647.

Redefine it to: print to stderr the commandline before spawning any child process.

Audit all uses of the verbose flag and all child process invocations.

zig/lib/build_runner.zig

Lines 117 to 118 in 68c7261

	if (mem.eql(u8, arg, "--verbose")) {
	builder.verbose = true;

zig/lib/build_runner.zig

Line 946 in 68c7261

\\ --verbose Print commands before executing them