elf: Reset alignment for each PT_LOAD segment

Reset alignment for each PT_LOAD segment to avoid using alignment from
the previous PT_LOAD segment.

bfd/

	PR ld/29435
	* elf.c (assign_file_positions_for_load_sections): Reset
	alignment for each PT_LOAD segment.

ld/

	PR ld/29435
	* testsuite/ld-elf/pr29435.d: New file.
	* testsuite/ld-elf/pr29435.s: Likewise.

(cherry picked from commit 59f21454)