Android NDK/Clang: fix implicit macro define

it reports:
criu/pie/util-vdso-elf32.c:255:8: error: implicit declaration of function 'ELF32_ST_TYPE' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
                        if (ELF_ST_TYPE(sym->st_info) != STT_FUNC &&
                            ^
criu/include/util-vdso.h:72:21: note: expanded from macro 'ELF_ST_TYPE'
                        ^
/opt/android-ndk/toolchains/llvm/prebuilt/linux-x86_64//sysroot/usr/include/linux/elf.h:114:26: note: expanded from macro 'ELF32_ST_TYPE'
                         ^
criu/include/util-vdso.h:72:21: note: expanded from macro 'ELF_ST_TYPE'

add #ifndef to check whether these macro is already defined.

Cc: Chen Hu <hu1.chen@intel.com>
Signed-off-by: Zhang Ning <ning.a.zhang@intel.com>
Reviewed-by: Dmitry Safonov <0x7f454c46@gmail.com>
Signed-off-by: Andrei Vagin <avagin@gmail.com>

criu/include/util-vdso.h

@@ -68,8 +68,12 @@ struct vdso_maps {
 #define Word_t		Elf32_Word
 #define Dyn_t		Elf32_Dyn
 
+#ifndef ELF_ST_TYPE
 #define ELF_ST_TYPE	ELF32_ST_TYPE
+#endif
+#ifndef ELF_ST_BIND
 #define ELF_ST_BIND	ELF32_ST_BIND
+#endif
 
 #else /* CONFIG_VDSO_32 */