MC: Add support for BigObj

Teach WinCOFFObjectWriter how to write -mbig-obj style object files;
these object files allow for more sections inside an object file.

Our support for BigObj is notably different from binutils and cl: we
implicitly upgrade object files to BigObj instead of asking the user to
compile the same file *again* but with another flag.  This matches up
with how LLVM treats ELF variants.

This was tested by forcing LLVM to always emit BigObj files and running
the entire test suite.  A specific test has also been added.

I've lowered the maximum number of sections in a normal COFF file,
VS "14" CTP 3 supports no more than 65279 sections.  This is important
otherwise we might not switch to BigObj quickly enough, leaving us with
a COFF file that we couldn't link.

yaml2obj support is all that remains to implement.

Differential Revision: http://reviews.llvm.org/D5349

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217812 91177308-0d34-0410-b5e6-96231b3b80d8

tools/llvm-objdump/llvm-objdump.cpp

@@ -591,6 +591,8 @@ static void PrintCOFFSymbolTable(const COFFObjectFile *coff) {
         if (error(coff->getAuxSymbol<coff_aux_section_definition>(SI + 1, asd)))
           return;
 
+        int32_t AuxNumber = asd->getNumber(Symbol->isBigObj());
+
         outs() << "AUX "
                << format("scnlen 0x%x nreloc %d nlnno %d checksum 0x%x "
                          , unsigned(asd->Length)
@@ -598,7 +600,7 @@ static void PrintCOFFSymbolTable(const COFFObjectFile *coff) {
                          , unsigned(asd->NumberOfLinenumbers)
                          , unsigned(asd->CheckSum))
                << format("assoc %d comdat %d\n"
-                         , unsigned(asd->Number)
+                         , unsigned(AuxNumber)
                          , unsigned(asd->Selection));
       } else if (Symbol->isFileRecord()) {
         const char *FileName;