Add Meson clang-format target

Since Meson doesn't have a way of specifying the working directory of a
command, I had to modify the script to make it cd into the source root
when ran from Meson.

You can run the format target with meson compile -C builddir format or
ninja -C builddir format

meson.build

@@ -115,3 +115,10 @@ endif
 if get_option('PISTACHE_BUILD_DOCS')
 	subdir('docs')
 endif
+
+if find_program('clang-format', required: false).found()
+	run_target(
+		'format',
+		command: (find_program('tools/format.sh'))
+	)
+endif

tools/format.sh

-#!/usr/bin/env bash
+#!/bin/sh
 
 set -eu
 
+if [ ! -z ${MESON_SOURCE_ROOT+x} ]; then cd "${MESON_SOURCE_ROOT}"; fi
+
 find_files() {
     git ls-files --cached --exclude-standard --others | grep -E '\.(cc|cpp|h)$'
 }