Fix building on MSYS2

Makefile.emscripten

@@ -3,15 +3,15 @@ AR       = emar
 LAUNCHER = start
 RM       = rm -rf
 MKDIR    = mkdir
+ECHO     = echo
 
-LIBS=
-CFLAGS= -s FULL_ES2=1 -s ASM_JS=1 -O1 -Wno-implicit-function-declaration
-#LDFLAGS= --embed-file data
-LDFLAGS= --preload-file data
+LIBS    =
+CFLAGS  = -s FULL_ES2=1 -s ASM_JS=1 -O1 -Wno-implicit-function-declaration -DEMSCRIPTEN
+LDFLAGS = --preload-file data
 
-RES_GAMELIB=libgame.a
-RES_GAME=game.html
-BUILDDIR=build-emscripten
+RES_GAMELIB = libgame.a
+RES_GAME    = game.html
+BUILDDIR    = build-emscripten
 
 ifeq ($(target),release)
 	CFLAGS= -s FULL_ES2=1 -s ASM_JS=1 -O2 --llvm-lto 1 -Wno-implicit-function-declaration