Update build system

build/Makefile

@@ -1,16 +1,28 @@
-all: gba_build sdl_build sdl_debug_build
+all: gba_build native_build native_debug_build windows_release windows_debug
+
+MAKE=make -j
 
 gba_build:
-	@if [ -d gba ]; then \
-		make -C gba ${ARGS}; \
+	@if [ -d gba-release ]; then \
+		${MAKE} -C gba-release ${ARGS}; \
 	fi
 
-sdl_build:
-	@if [ -d sdl ]; then \
-		make -C sdl ${ARGS}; \
+native_build:
+	@if [ -d ${TARGET}-release ]; then \
+		${MAKE} -C ${TARGET}-release ${ARGS}; \
 	fi
 
-sdl_debug_build:
-	@if [ -d sdl_debug ]; then \
-		make -C sdl_debug ${ARGS}; \
+native_debug_build:
+	@if [ -d ${TARGET}-debug ]; then \
+		${MAKE} -C ${TARGET}-debug ${ARGS}; \
+	fi
+
+windows_release:
+	@if [ -d windows-release ]; then \
+		${MAKE} -C windows-release ${ARGS}; \
+	fi
+
+windows_debug:
+	@if [ -d windows-debug ]; then \
+		${MAKE} -C windows-debug ${ARGS}; \
 	fi