testsuite: Rename test-defined macros

testsuite: Rename test-defined macros

Epiphany, PRU, ARC and NDS32 may predefine __big_endian__ and
__little_endian__ macros.  This leads to spurious warnings like:
  gcc.dg/sso/memcpy-1.c:7: warning: "__little_endian__" redefined

Fix by renaming the macros in the test.

gcc/testsuite/ChangeLog:

	* gcc.dg/sso/memcpy-1.c (__big_endian__, __little_endian__):
	Rename macros to avoid conflicts with predefined ones.

Signed-off-by: Dimitar Dimitrov <dimitar@dinux.eu>