Add Darwin-target for building vendor/stb macos universal libs

This Darwin-specific target builds each stb library with macOS-specific
options so that the results are universal static libraries that should
work on Intel (x86_64) and Apple Silicon (arm64) machines. They also
should work on macOS 10.12 and above (which should match what Odin
compiles for).

The default Makefile target will build the darwin rule if its invoked on
a macOS machine, otherwise it'll invoke the more general unix target.

vendor/stb/src/Makefile

@@ -1,4 +1,12 @@
-all:
+OS=$(shell uname)
+
+ifeq ($(OS), Darwin)
+all: darwin
+else
+all: unix
+endif
+
+unix:
 	mkdir -p ../lib
 	$(CC) -c -O2 -Os -fPIC stb_image.c stb_image_write.c stb_image_resize.c stb_truetype.c stb_rect_pack.c stb_vorbis.c
 	$(AR) rcs ../lib/stb_image.a        stb_image.o
@@ -14,3 +22,25 @@ all:
 	#$(CC) -fPIC -shared -Wl,-soname=stb_rect_pack.so     -o ../lib/stb_rect_pack.so    stb_rect_packl.o
 	#$(CC) -fPIC -shared -Wl,-soname=stb_vorbis.so        -o ../lib/stb_vorbis.so       stb_vorbisl.o
 	rm *.o
+
+darwin:
+	mkdir -p ../lib
+	$(CC) -arch x86_64 -c -O2 -Os -fPIC stb_image.c -o stb_image-x86_64.o -mmacosx-version-min=10.12
+	$(CC) -arch arm64  -c -O2 -Os -fPIC stb_image.c -o stb_image-arm64.o -mmacosx-version-min=10.12
+	lipo -create stb_image-x86_64.o stb_image-arm64.o -output ../lib/darwin/stb_image.a
+	$(CC) -arch x86_64 -c -O2 -Os -fPIC stb_image_write.c -o stb_image_write-x86_64.o -mmacosx-version-min=10.12
+	$(CC) -arch arm64  -c -O2 -Os -fPIC stb_image_write.c -o stb_image_write-arm64.o -mmacosx-version-min=10.12
+	lipo -create stb_image_write-x86_64.o stb_image_write-arm64.o -output ../lib/darwin/stb_image_write.a
+	$(CC) -arch x86_64 -c -O2 -Os -fPIC stb_image_resize.c -o stb_image_resize-x86_64.o -mmacosx-version-min=10.12
+	$(CC) -arch arm64  -c -O2 -Os -fPIC stb_image_resize.c -o stb_image_resize-arm64.o -mmacosx-version-min=10.12
+	lipo -create stb_image_resize-x86_64.o stb_image_resize-arm64.o -output ../lib/darwin/stb_image_resize.a
+	$(CC) -arch x86_64 -c -O2 -Os -fPIC stb_truetype.c -o stb_truetype-x86_64.o -mmacosx-version-min=10.12
+	$(CC) -arch arm64  -c -O2 -Os -fPIC stb_truetype.c -o stb_truetype-arm64.o -mmacosx-version-min=10.12
+	lipo -create stb_truetype-x86_64.o stb_truetype-arm64.o -output ../lib/darwin/stb_truetype.a
+	$(CC) -arch x86_64 -c -O2 -Os -fPIC stb_rect_pack.c -o stb_rect_pack-x86_64.o -mmacosx-version-min=10.12
+	$(CC) -arch arm64  -c -O2 -Os -fPIC stb_rect_pack.c -o stb_rect_pack-arm64.o -mmacosx-version-min=10.12
+	lipo -create stb_rect_pack-x86_64.o stb_rect_pack-arm64.o -output ../lib/darwin/stb_rect_pack.a
+	$(CC) -arch x86_64 -c -O2 -Os -fPIC stb_vorbis.c -o stb_vorbis-x86_64.o -mmacosx-version-min=10.12
+	$(CC) -arch arm64  -c -O2 -Os -fPIC stb_vorbis.c -o stb_vorbis-arm64.o -mmacosx-version-min=10.12
+	lipo -create stb_vorbis-x86_64.o stb_vorbis-arm64.o -output ../lib/darwin/stb_vorbis.a
+	rm *.o