PowerPC: Skip base type RTTI tests before inferior start

On PowerPC targets, RTTI typeinfo objects for simple base types such as
`int`, `char*`, and `const char*` may not be emitted until the inferior
has been started.  As a result, the `gdb.cp/typeid.exp` test fails when
checking typeid results before program execution begins.

This patch extends the existing Clang-specific logic that skips base type
RTTI checks before the inferior starts, to also apply on PowerPC.  This
ensures consistent test behavior across compilers and targets.

gdb/testsuite/
    * gdb.cp/typeid.exp (do_typeid_tests): Skip base type RTTI tests
    before inferior start on PowerPC.

Approved-By: Tom de Vries <tdevries@suse.de>