Adding dllimport, dllexport and external weak linkage types.
DLL* linkages got full (I hope) codegeneration support in C & both x86
assembler backends.
External weak linkage added for future use, we don't provide any
codegeneration, etc. support for it.

llvm-svn: 30374
29 files changed
tree: d472b468851ea4e3a4700c6d626fb1049cbbf29a
  1. llvm/