Add a Makefile for build tasks

Makefile

@@ -0,0 +1,13 @@
+INSTALLDIR := /usr/share/libretro/shaders/shaders_slang
+
+all:
+	@echo "Nothing to make for slang-shaders."
+
+install:
+	mkdir -p $(DESTDIR)$(INSTALLDIR)
+	cp -ar -t $(DESTDIR)$(INSTALLDIR) *
+	rm -f $(DESTDIR)$(INSTALLDIR)/Makefile \
+		$(DESTDIR)$(INSTALLDIR)/configure
+
+test-install: all
+	DESTDIR=/tmp/build $(MAKE) install

configure

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+PACKAGE_NAME=slang-shaders