* ldlang.c (lang_new_phdr): Check PHDRS and FILEHDR in loadable
segments do not appear after a different loadable segment.
* ld.texinfo (PHDRS): Document order of processing segments.
Document where PHDRS and FILEHDR may appear.
ld/testsuite/
* ld-scripts/phdrs3.d: New.
* ld-scripts/phdrs3.t: New.
* ld-scripts/phdrs3.exp: New.