Emit the string information for the asm writer as a single large string

Emit the string information for the asm writer as a single large string
and index into it, instead of emitting it like this:

  static const char * const OpStrs[] = {
    "PHINODE\n",        // PHI
    0,  // INLINEASM
    "adc ",     // ADC32mi
    "adc ",     // ADC32mi8
   ...

The old way required thousands of relocations that slows down link time and
dynamic load times.

This also cuts about 10K off each of the X86 asmprinters, and should shrink
the others as well.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@29152 91177308-0d34-0410-b5e6-96231b3b80d8