Fix and enable EH for x86-64 Darwin.  Adds
ShortenEHDataFor64Bits as a not-very-accurate
abstraction to cover all the changes in DwarfWriter.
Some cosmetic changes to Darwin assembly code for
gcc testsuite compatibility.

llvm-svn: 46029
diff --git a/llvm/lib/Target/PowerPC/PPCTargetAsmInfo.cpp b/llvm/lib/Target/PowerPC/PPCTargetAsmInfo.cpp
index e593482..8728def 100644
--- a/llvm/lib/Target/PowerPC/PPCTargetAsmInfo.cpp
+++ b/llvm/lib/Target/PowerPC/PPCTargetAsmInfo.cpp
@@ -50,6 +50,7 @@
     StaticCtorsSection = ".mod_init_func";
     StaticDtorsSection = ".mod_term_func";
   }
+  SwitchToSectionDirective = "\t.section ";
   UsedDirective = "\t.no_dead_strip\t";
   WeakDefDirective = "\t.weak_definition ";
   WeakRefDirective = "\t.weak_reference ";