jar_xm: Workaround for unaligned pointer accesses

jar_xm.h does some shady pointer casts leading to unaligned accesses
and breaking strict aliasing. x86 has special circuitry for doing
unaligned accesses, but on other architectures, it may trap and require
kernel fix-up or crash outright. With this patch, one obstacle in
porting raylib to the GameBoy Advance has been removed. Go for it ;-)

To avoid having to rewrite that `mempool' code, insert padding before
structs and instruct the compiler (GCC, most importantly), to be gentle
when optimizing.

This fixes #490 (Unless we got ourselves 256-bit pointers, if so,
hello future!)

src/Makefile

@@ -291,7 +291,9 @@ endif
 #  -Wno-missing-braces   ignore invalid warning (GCC bug 53119)
 #  -D_DEFAULT_SOURCE     use with -std=c99 on Linux and PLATFORM_WEB, required for timespec
 #  -Werror=pointer-arith catch unportable code that does direct arithmetic on void pointers
-CFLAGS += -O1 -Wall -std=c99 -D_DEFAULT_SOURCE -Wno-missing-braces -Werror=pointer-arith
+#  -fno-strict-aliasing  jar_xm.h does shady stuff (breaks strict aliasing)
+CFLAGS += -O1 -Wall -std=c99 -D_DEFAULT_SOURCE -Wno-missing-braces -Werror=pointer-arith 
+-fno-strict-aliasing
 
 ifeq ($(RAYLIB_BUILD_MODE), DEBUG)
     CFLAGS += -g