Makefile, .gitignore, .editorconfig, configure, tests/cc-compat.sh: added configure script for compiler optimizations

configure

@@ -0,0 +1,39 @@
+#!/bin/sh
+
+# Copyright (c) 2023–2024 Emma Tebibyte <emma@tebibyte.media>
+# SPDX-License-Identifier: FSFAP
+#
+# Copying and distribution of this file, with or without modification, are
+# permitted in any medium without royalty provided the copyright notice and this
+# notice are preserved.  This file is offered as-is, without any warranty.
+
+set -e
+
+CFLAGS='-Lbuild/lib -idirafter include -O3'
+RUSTFLAGS='-Copt-level=z -Ccodegen-units=1 -Cpanic=abort -Clto=y \
+	-Cstrip=symbols -Ctarget-cpu=native \
+	--extern sysexits=build/o/libsysexits.rlib'
+
+case "$@" in
+	clang)
+		CFLAGS="$CFLAGS -Wall"
+		;;
+	clean)
+		rm *.mk || true
+		exit 0
+		;;
+	gcc)
+		CFLAGS="$CFLAGS -s -Wl,-z,noseparate-code,-z,nosectionheader -flto"
+		;;
+	'rustc +nightly')
+		RUSTFLAGS="+nightly -Zlocation-detail=none $RUSTFLAGS"
+		;;
+	'') ;;
+	*)
+		printf 'Usage: %s [compiler]\n' "$0"
+		exit 64 # sysexits.h(3) EX_USAGE
+		;;
+esac
+
+printf 'CFLAGS=%s\n' "$CFLAGS" >cc.mk
+printf 'RUSTFLAGS=%s\n' "$RUSTFLAGS" >rustc.mk