ld: Xfail PR ld/26936 test if not supported

Linkonce sections and comdat groups can be mixed only if comdat groups
have only a single member with matching symbol table entries.  Xfail
ld/26936 test:

1. If comdat groups always have more than one member.
2. If symbol table entries in linkonce and comdat group don't match.
3. If the assembly source file is renamed.

	PR ld/26936
	* testsuite/ld-elf/pr26936.d: Xfail targets which don't support
	mixing linkonce and comdat sections.

ld/ChangeLog

@@ -1,3 +1,9 @@
+2020-11-29  H.J. Lu  <hongjiu.lu@intel.com>
+
+	PR ld/26936
+	* testsuite/ld-elf/pr26936.d: Xfail targets which don't support
+	mixing linkonce and comdat sections.
+
 2020-11-28  Alan Modra  <amodra@gmail.com>
 
 	* testsuite/ld-elf/pr26907.ld,

ld/testsuite/ld-elf/pr26936.d

@@ -5,6 +5,13 @@
 #ld: -z noseparate-code -Ttext-segment 0x10000 -z max-page-size=0x1000
 #readelf: -wL
 #target: [check_shared_lib_support]
+# Assembly source file for the HPPA assembler is renamed and modifed by
+# sed.  mn10300 and riscv put different numbers of local symbols in
+# linkonce section and comdat sections.  Some MIPS targets put section
+# names in symbol table.  xtensa has more than one member in comdat
+# groups.
+#xfail: am33_2.0-*-* hppa*-*-hpux* mips*-*-elf mips*-*-irix*
+#xfail: mn10300-*-* tx39*-*-* riscv*-*-* xtensa*-*-*
 
 #...
 CU: .*/pr26936c.s: