selftests/powerpc/ptrace: Build the ptrace-gpr test as 32-bit when possible

The ptrace-gpr test can now be built 32-bit, so do that if that's the
compiler default rather than forcing a 64-bit build.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220627140239.2464900-9-mpe@ellerman.id.au

tools/testing/selftests/powerpc/ptrace/Makefile

@@ -11,7 +11,6 @@ TM_TESTS += ptrace-tm-vsx
 TESTS_64 := $(TM_TESTS)
 TESTS_64 += core-pkey
 TESTS_64 += perf-hwbreak
-TESTS_64 += ptrace-gpr
 TESTS_64 += ptrace-hwbreak
 TESTS_64 += ptrace-perf-hwbreak
 TESTS_64 += ptrace-pkey
@@ -19,7 +18,9 @@ TESTS_64 += ptrace-syscall
 TESTS_64 += ptrace-tar
 TESTS_64 += ptrace-vsx
 
-TEST_GEN_PROGS := $(TESTS_64)
+TESTS += ptrace-gpr
+
+TEST_GEN_PROGS := $(TESTS) $(TESTS_64)
 
 LOCAL_HDRS += $(patsubst %,$(selfdir)/powerpc/ptrace/%,$(wildcard *.h))