elf: Add a test for PT_LOAD segments with mixed p_align [BZ #28676]

Add tst-p_alignmod1-edit to edit the copy of tst-p_alignmod-base.so to
reduce p_align of the first PT_LOAD segment by half and verify that the
shared library is mapped with the maximum p_align of all PT_LOAD segments.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>