SEC_EXCLUDE is ignored when doing a relocatable link. But we can't
merge 2 input sections with the same name when only one of them has
SHF_EXCLUDE.
PR ld/20528
* emultempl/elf32.em (gld${EMULATION_NAME}_place_orphan): Don't
merge 2 sections with different SHF_EXCLUDE.
* testsuite/ld-elf/pr20528a.d: New file.
* testsuite/ld-elf/pr20528a.s: Likewise.
* testsuite/ld-elf/pr20528b.d: Likewise.
* testsuite/ld-elf/pr20528b.s: Likewise.
