Greatly simplify error handling in shell scripts

Instead of having detailed error messages, run most
commands through a function that calls err() under
fault conditions.

Where detail is still required, err() is still called
manually. Where it isn't, the error message is simply
whatever command was executed to cause the error.

This results in a massive sloccount reduction for lbmk;
specifically, 178 sloc reduction, or a 8.1% reduction.
The total sloccount is now 2022, for shell scripts.

Signed-off-by: Leah Rowe <leah@libreboot.org>

include/err.sh

@@ -1,6 +1,15 @@
 # SPDX-License-Identifier: MIT
 # SPDX-FileCopyrightText: 2022, 2023 Leah Rowe <leah@libreboot.org>
 
+xfail=""
+
+x_() {
+	[ $# -lt 1 ] || ${@} || err "${@}"
+}
+xx_() {
+	[ $# -lt 1 ] || ${@} || fail "${@}"
+}
+
 setvars()
 {
 	_setvars=""