glib-2.0: Fix TMPDIR mismatch test failures

glib-2.0: Fix TMPDIR mismatch test failures

gcc 13 appears to trigger TMPDIR changes in glib which causes ptest failures:

FAIL: glib/utils-c-90.test (Child process killed by signal 6)
FAIL: glib/utils.test (Child process killed by signal 6)
FAIL: glib/utils-c-99.test (Child process killed by signal 6)
FAIL: glib/utils-c-17.test (Child process killed by signal 6)
FAIL: glib/utils-c-11.test (Child process killed by signal 6)

The issue is caused by our symlinks between tmp directories which
cause the tests to get confused. We can set G_TEST_TMPDIR to
a resolved path using readlink to avoid the failures.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>