llvm: Improve bitcode writer method dispatch

* sources/lib/llvm/llvm-bitcode.dylan (write-module): Declare the
  proper type of llvm-module-functions elements.

* sources/lib/llvm/bitcode.dylan
  (stream-record-id): Add type declarations for bitcode-records
   elements.
  (write-abbrev-record): Add type declarations for
   bitcode-abbrev-definitions entries and abbrev-ops elements.

sources/lib/llvm/bitcode.dylan

@@ -348,14 +348,15 @@ end bitcode-block;
 define method stream-record-id
     (stream :: <bitcode-stream>, record :: <symbol>)
  => (id :: <integer>)
-  let record-definition = element(stream.bitcode-records, record, default: #f);
-  if (~record-definition)
+  let record-definition :: false-or(<bitcode-record-definition>)
+    = element(stream.bitcode-records, record, default: #f);
+  if (record-definition)
+    record-definition.record-id
+  else
     error("record %= not defined for this block type", record);
-  end if;
-  record-definition.record-id
+  end if
 end method;
 
-
 /// Abbreviations
 
 define class <abbrev-op> (<object>)
@@ -493,7 +494,8 @@ end method;
 define method write-abbrev-record
   (stream :: <bitcode-stream>, name :: <symbol>, #rest operands)
  => ();
-  let definition = stream.bitcode-abbrev-definitions[name];
+  let definition :: <bitcode-abbrev-definition>
+    = stream.bitcode-abbrev-definitions[name];
 
   // Output the abbreviation id
   write-abbrev-id(stream, definition.abbrev-id);
@@ -503,7 +505,7 @@ define method write-abbrev-record
   for (value in operands,
        op-index = 0
          then begin
-                let op = ops[op-index];
+                let op :: <abbrev-op> = ops[op-index];
                 select (op.op-kind)
                   #"fixed" =>
                     write-fixed(stream, op.op-data, value);
@@ -513,7 +515,7 @@ define method write-abbrev-record
                     op-index + 1;
                   #"array" =>
                     write-vbr(stream, 6, value.size);
-                    let aop = ops[op-index + 1];
+                    let aop :: <abbrev-op> = ops[op-index + 1];
                     select (aop.op-kind)
                       #"fixed" =>
                         do(curry(write-fixed, stream, aop.op-data), value);

sources/lib/llvm/llvm-bitcode.dylan

@@ -2823,7 +2823,7 @@ define function write-module
             write-record(stream, #"GCNAME", gc-name);
           end if;
         end method;
-      for (global :: <llvm-global-value> in m.llvm-module-functions)
+      for (global :: <llvm-function> in m.llvm-module-functions)
         if (global.llvm-function-garbage-collector)
           do-gc(global.llvm-function-garbage-collector);
         end if;