ld: Rewrite lang_size_relro_segment_1

1. Compute the desired PT_GNU_RELRO segment base and find the maximum
section alignment of sections starting from the PT_GNU_RELRO segment.
2. Find the first preceding load section.
3. Don't add the 1-page gap between the first preceding load section and
the relro segment if the maximum page size >= the maximum section
alignment.  Align the PT_GNU_RELRO segment first.  Subtract the maximum
page size if therer is still a 1-page gap.

	PR ld/28743
	PR ld/28819
	* ldlang.c (lang_size_relro_segment_1): Rewrite.
	* testsuite/ld-x86-64/pr28743-1.d: New file.
	* testsuite/ld-x86-64/pr28743-1.s: Likewise.
	* testsuite/ld-x86-64/x86-64.exp: Run pr28743-1.