ndk: Add crtbrand.c ; crtbegin_static.S includes "atexit.S" for x86/mips

"atexit" isn't defined in libc.a for x86/mips (unlike their arm's counterpart).
Include atexit.S otherwise app using atexit() may fail to link statically.

Also, add crtbegin.c to brand crtbegin_static/dynamic.c with .note.ABI-tag
section of given API level.  See $NDK/gen-platforms.sh

Change-Id: I2fdbb92119e3ca2da2c1ced6d77e63136ec35c34

ndk/platforms/android-9/arch-x86/src/crtbegin_dynamic.S

@@ -60,10 +60,9 @@ _start:
         mov     $0, %edx
         pushl   %edx
         pushl   %eax
-        call     __libc_init
+        call    __libc_init
 
-0:
-        jmp   main
+0:  jmp   main
 
 1:  .long   __PREINIT_ARRAY__
     .long   __INIT_ARRAY__