testsuite: XFAIL linkage testcases on AIX.

The template linkage2.C and linkage3.C testcases expect a
decoration that does not match AIX assembler syntax.  Expect failure.

gcc/testsuite/ChangeLog:
	* g++.dg/template/linkage2.C: XFAIL on AIX.
	* g++.dg/template/linkage3.C: Same.

Signed-off-by: David Edelsohn <dje.gcc@gmail.com>

gcc/testsuite/g++.dg/template/linkage2.C

 // PR c++/70413
 // { dg-do compile { target c++11 } }
-// { dg-final { scan-assembler-not "(weak|glob)\[^\n\]*_Z" } }
+// { dg-final { scan-assembler-not "(weak|glob)\[^\n\]*_Z" { xfail powerpc-*-aix* } } }
 
 namespace {
   template<class> struct A;

gcc/testsuite/g++.dg/template/linkage3.C

 // PR c++/70413
-// { dg-final { scan-assembler-not "(weak|glob)\[^\n\]*_Z" } }
+// { dg-final { scan-assembler-not "(weak|glob)\[^\n\]*_Z" { xfail powerpc-*-aix* } } }
 
 namespace {
   struct A {