meson: use "sh -eu" and make .sh +x, .py -x

Shell scripts should be executable so that meson reports their
invocation succinctly (does not print 'sh' '-e').
Python scripts should not be executable so that meson does the
detection of the right python binary itself.

Add -u everywhere to catch potential errors.

tools/meson-check-compilation.sh

@@ -1,3 +1,3 @@
-#!/bin/sh -e
+#!/bin/sh -eu
 
 "$@" '-' '-c' -o/dev/null </dev/null

tools/meson-check-help.sh

@@ -1,4 +1,4 @@
-#!/bin/sh -e
+#!/bin/sh -eu
 
 # output width
 if "$1"  --help | grep -v 'default:' | grep -E -q '.{80}.'; then

tools/meson-git-contrib.sh

@@ -1,4 +1,4 @@
-#!/bin/sh -e
+#!/bin/sh -eu
 
 git shortlog -s `git describe --abbrev=0`.. | \
     cut -c8- | \

tools/meson-hwdb-update.sh

@@ -1,4 +1,4 @@
-#!/bin/sh -ex
+#!/bin/sh -eu
 
 cd "$1"
 

tools/meson-make-symlink.sh

@@ -1,4 +1,4 @@
-#!/bin/sh -e
+#!/bin/sh -eu
 
 # this is needed mostly because $DESTDIR is provided as a variable,
 # and we need to create the target directory...