Add IR support, ELF section and user documentation for partitioning feature.

The partitioning feature was proposed here:
http://lists.llvm.org/pipermail/llvm-dev/2019-February/130583.html

This is mostly just documentation. The feature itself will be contributed
in subsequent patches.

Differential Revision: https://reviews.llvm.org/D60242

llvm-svn: 361923
diff --git a/llvm/lib/MC/MCParser/ELFAsmParser.cpp b/llvm/lib/MC/MCParser/ELFAsmParser.cpp
index 48ced8d..a55bdd5 100644
--- a/llvm/lib/MC/MCParser/ELFAsmParser.cpp
+++ b/llvm/lib/MC/MCParser/ELFAsmParser.cpp
@@ -617,6 +617,8 @@
       Type = ELF::SHT_LLVM_CALL_GRAPH_PROFILE;
     else if (TypeName == "llvm_dependent_libraries")
       Type = ELF::SHT_LLVM_DEPENDENT_LIBRARIES;
+    else if (TypeName == "llvm_sympart")
+      Type = ELF::SHT_LLVM_SYMPART;
     else if (TypeName.getAsInteger(0, Type))
       return TokError("unknown section type");
   }