work-around system header namespace pollution

Including limits.h on vxworks pollutes the global namespace with SH
and many other platform names; work around it.


for  gcc/testsuite/ChangeLog

	* gcc.target/aarch64/vect-mull.x (SH): Undefine.

gcc/testsuite/ChangeLog

+2020-02-27  Alexandre Oliva <oliva@adacore.com>
+
+	* gcc.target/aarch64/vect-mull.x (SH): Undefine.
+
 2020-02-27  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/93508

gcc/testsuite/gcc.target/aarch64/vect-mull.x

@@ -9,6 +9,7 @@ typedef unsigned short *__restrict__ pRUINT16;
 typedef unsigned int *__restrict__ pRUINT32;
 typedef unsigned long long *__restrict__ pRUINT64;
 
+#undef SH /* Including limits.h on vxworks defines this.  */
 typedef signed short SH;
 typedef unsigned short UH;
 typedef signed int SS;