testsuite: mallign: Handle word size of 1 byte

testsuite: mallign: Handle word size of 1 byte

This patch fixes a spurious warning for the pru-unknown-elf target:
  gcc/testsuite/gcc.dg/mallign.c:12:27: warning: ignoring return value of 'malloc' declared with attribute 'warn_unused_result' [-Wunused-result]

For 8-bit targets the resulting mask ignores all bits in the value
returned by malloc.  Fix by first checking the target word size.

gcc/testsuite/ChangeLog:

	* gcc.dg/mallign.c: Skip check if sizeof(word)==1.

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