[testsuite] [analyzer] skip access-mode: O_ACCMODE on vxworks

O_ACCMODE is not defined on vxworks, and the test is meaningless and
failing without it, so skip it.


for  gcc/testsuite/ChangeLog

	* gcc.dg/analyzer/fd-access-mode-target-headers.c: Skip on
	vxworks as well.

gcc/testsuite/gcc.dg/analyzer/fd-access-mode-target-headers.c

-/* { dg-skip-if "" { powerpc*-*-aix* || newlib } } */
-/* { dg-skip-if "" { avr-*-* } } */
+/* { dg-skip-if "" { { powerpc*-*-aix* avr-*-* *-*-vxworks* } || newlib } } */
 
 #include <sys/stat.h>
 #include <fcntl.h>