LLVM: Add ELF Note section to NaCl object files identifying them as such to gold

test/MC/X86/elf-note-nacl.s

+# RUN: llvm-mc -filetype=obj -triple i686-none-nacl %s -o - \
+# RUN:   | llvm-objdump -triple i686 -s - | FileCheck --check-prefix=I386 %s
+
+# RUN: llvm-mc -filetype=obj -triple x86_64-none-nacl %s -o - \
+# RUN:   | llvm-objdump -triple x86_64 -s - | FileCheck --check-prefix=X8664 %s
+
+# Tests that NaCl object files contain an ELF note section that identifies them
+# to the binutils gold linker
+
+  .text
+foo:
+  ret
+
+# There appears to be no way for llvm-objdump to show flags for sections, or
+# to dump groups like readelf
+# I386: .group        
+# I386: .note.NaCl.ABI.x86-32
+# contents of the words in the note section should be:
+# sizeof "NaCl"
+# sizeof "x86-32"
+# 1 (NT_VERSION)
+# "NaCl" with nul termination and padding to align 4
+# "x86-32" with nul termination and padding to align 4
+# I386-NEXT: 0000 05000000 07000000 01000000 4e61436c
+# I386-NEXT: 0010 00000000 7838362d 33320000
+
+# X8664: .group        
+# X8664: .note.NaCl.ABI.x86-64
+# contents of the words in the note section should be:
+# sizeof "NaCl"
+# sizeof "x86-64"
+# 1 (NT_VERSION)
+# "NaCl" with nul termination and padding to align 4
+# "x86-64" with nul termination and padding to align 4
+# X8664-NEXT: 0000 05000000 07000000 01000000 4e61436c
+# X8664-NEXT: 0010 00000000 7838362d 36340000