Load multiple object files and link them via RuntimeDyld in llvm-rtdyld.

Relocations between the object modules are properly resolved, as in the
following trivial example:

$ cat t.c
int foo();
int main() {
    return foo();
}
$ cat foo.c
int foo() {
    return 65;
}
$ clang -c t.c -fno-asynchronous-unwind-tables
$ clang -c foo.c -fno-asynchronous-unwind-tables
$ llvm-rtdyld t.o foo.o ; echo $?
loaded '_main' at: 0x10015c000
65

llvm-svn: 129448