Assemble calls to constant addresses.

Finally address this TODO in the assembler. This will help translate
non-IRT using programs (no ABI stability). The default scons testing
mode is non-IRT, so this helps with that. I haven't actually tested
this against scons yet, but I'm filling in the tests based on how
LLVM translates the same bitcode.

The filetype=asm is adjusted to omit the "*" and the "$".

The filetype=obj is adjusted to check for fixups with NullSymbols,
and also fill the assembler buffer at the instruction's immediate
field w/ the right constant.

The filetype=iasm is still TODO (hits an new assert in the Fixup's emit() function).

Reverts 7ad1bed99d058199a3ba246a5383458518596fbc:
"Allow stubbing of called constant addresses using command line argument."
since this is now handled (except for iasm).

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4080
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/1017373002

src/IceELFSection.cpp

diff --git a/src/IceELFSection.cpp b/src/IceELFSection.cpp
index f2e129d..4ca2de4 100644
--- a/src/IceELFSection.cpp
+++ b/src/IceELFSection.cpp
@@ -80,6 +80,15 @@
 
 // Symbol tables.
 
+void ELFSymbolTableSection::createNullSymbol(ELFSection *NullSection) {
+  // The first entry in the symbol table should be a NULL entry,
+  // so make sure the map is still empty.
+  assert(LocalSymbols.empty());
+  const IceString NullSymName("");
+  createDefinedSym(NullSymName, STT_NOTYPE, STB_LOCAL, NullSection, 0, 0);
+  NullSymbol = findSymbol(NullSymName);
+}
+
 void ELFSymbolTableSection::createDefinedSym(const IceString &Name,
                                              uint8_t Type, uint8_t Binding,
                                              ELFSection *Section,
@@ -105,7 +114,9 @@
   NewSymbol.Sym.setBindingAndType(STB_GLOBAL, STT_NOTYPE);
   NewSymbol.Section = NullSection;
   NewSymbol.Number = ELFSym::UnknownNumber;
-  GlobalSymbols.insert(std::make_pair(Name, NewSymbol));
+  bool Unique = GlobalSymbols.insert(std::make_pair(Name, NewSymbol)).second;
+  assert(Unique);
+  (void)Unique;
 }
 
 const ELFSym *ELFSymbolTableSection::findSymbol(const IceString &Name) const {