Added llvm support for current version 18. This is for reference only

as the bindings cannot be compiled without a couple of changes to llvm
itself. Which I plan to do. These are to do with debug support for
dynamic arrays and subranges. You could possibly comment them out if
you are keen to try. Also this version supports the major change llvm
made to support opaque pointers. As a result m3 llvm is slightly simpler
especially in doing loads and stores. In the IR you will now see things
like ptr somevar instead of i64* somevar. A lot of bitcasts bewteen
i8* and i64* have become redundant.

m3-sys/llvm/llvm18/src/M3CG_LLVM.i3

@@ -0,0 +1,22 @@
+INTERFACE M3CG_LLVM;
+
+IMPORT M3CG,Wr;
+
+TYPE
+  U <: Public;
+
+  Public = M3CG.T OBJECT
+  METHODS
+    dumpLLVMIR(BitcodeFileName, AsmFileName: TEXT);
+  END;
+
+TYPE m3llvmDebugLevTyp = [ 0 .. 5 ]; (* Just leave some space here. *) 
+
+(* returns a fresh, initialized code generator that writes LLVM IR
+   as bitcode to 'wr_bin' and as LLVM assembly to 'wr_char'. 
+   Either may be NIL. *)
+PROCEDURE New 
+  (output: Wr.T; targetTriple,dataRep : TEXT; m3llvmDebugLev: m3llvmDebugLevTyp; genDebug: BOOLEAN)
+: M3CG.T; 
+
+END M3CG_LLVM.