Fix a bug that would cause subzero to fail when --threads=0.

src/IceELFObjectWriter.h

Index: src/IceELFObjectWriter.h
diff --git a/src/IceELFObjectWriter.h b/src/IceELFObjectWriter.h
index 11038455616eab6a33b44ea83a8c67c58fd53bd1..333aa075f9dda987e39f9f9bde60e0e70fc07a71 100644
--- a/src/IceELFObjectWriter.h
+++ b/src/IceELFObjectWriter.h
@@ -30,7 +30,8 @@ namespace Ice {
 // sections and write them out.  Expected usage:
 //
 // (1) writeInitialELFHeader (invoke once)
-// (2) writeDataSection  (invoke once)
+// (2) writeDataSection  (may be invoked multiple times, as long as
+//     SectionSuffix is unique)
 // (3) writeFunctionCode (must invoke once per function)
 // (4) writeConstantPool (must invoke once per pooled primitive type)
 // (5) setUndefinedSyms (invoke once)
@@ -43,10 +44,7 @@ namespace Ice {
 // variable is in a separate section and therefore the sections will be
 // trivially contiguous.
 //
-// The motivation for requiring that writeFunctionCode happen after
-// writeDataSection: to keep the .text and .data sections contiguous in the
-// file. Having both -fdata-sections and -ffunction-sections does allow
-// relaxing this requirement.
+// TODO(jpp): explain what's going on here.
 class ELFObjectWriter {
   ELFObjectWriter() = delete;
   ELFObjectWriter(const ELFObjectWriter &) = delete;
@@ -64,7 +62,8 @@ public:
   // of each global's definition in the symbol table.
   // Use the given target's RelocationKind for any relocations.
   void writeDataSection(const VariableDeclarationList &Vars,
-                        FixupKind RelocationKind);
+                        FixupKind RelocationKind,
+                        const IceString &SectionSuffix);
 
   // Copy data of a function's text section to file and note the offset of the
   // symbol's definition in the symbol table.
@@ -151,7 +150,8 @@ private:
   // SectionType, given the global variables Vars belonging to that SectionType.
   void writeDataOfType(SectionType SectionType,
                        const VariableDeclarationList &Vars,
-                       FixupKind RelocationKind);
+                       FixupKind RelocationKind,
+                       const IceString &SectionSuffix);
 
   // Write the final relocation sections given the final symbol table.
   // May also be able to seek around the file and resolve function calls