tools include linux: Guard against redefinition of some macros

When cross building to android r15c (and older versions) on Fedora 26
we notice these:

/opt/android-ndk-r15c/platforms/android-24/arch-arm/usr/include/sys/cdefs.h:332:0: note: this is the location of the previous definition

For __aligned, __packed and __noreturn, so guard those with ifdefs to
avoid drowning useful warnings in these.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-d7w3fa9c22dtmrwbedos6ie1@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/include/linux/compiler-gcc.h

@@ -21,11 +21,14 @@
 #define __must_be_array(a)	BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
 
 #define  noinline	__attribute__((noinline))
-
+#ifndef __packed
 #define __packed	__attribute__((packed))
-
+#endif
+#ifndef __noreturn
 #define __noreturn	__attribute__((noreturn))
-
+#endif
+#ifndef __aligned
 #define __aligned(x)	__attribute__((aligned(x)))
+#endif
 #define __printf(a, b)	__attribute__((format(printf, a, b)))
 #define __scanf(a, b)	__attribute__((format(scanf, a, b)))