Remove the old library names. These were unused since rustboot.

Right now rustc hardcodes -lrustllvm. The idea is to instead remember all the native
modules used and convert them to -l directives to the linker. In the case of a
library that is installed in an unusual location, Graydon suggested using metadata:

native module foo = "bar" {
}

src/comp/lib/llvm.rs

@@ -125,7 +125,7 @@ const uint LLVMRealULT = 12u;
 const uint LLVMRealULE = 13u;
 const uint LLVMRealUNE = 14u;
 
-native mod llvm = llvm_lib {
+native mod llvm = "rustllvm" {
 
     type ModuleRef;
     type ContextRef;
@@ -883,9 +883,6 @@ native mod llvm = llvm_lib {
     fn LLVMLinkModules(ModuleRef Dest, ModuleRef Src) -> Bool;
 }
 
-native mod rustllvm = llvm_lib {
-}
-
 /* Slightly more terse object-interface to LLVM's 'builder' functions. For the
  * most part, build.Foo() wraps LLVMBuildFoo(), threading the correct
  * BuilderRef B into place.  A BuilderRef is a cursor-like LLVM value that