asm: add test cases for LLVM 10.0

This includes test cases for the use of nofree as parameter attribute
and the new calling conventions of LLVM 10.0.

Updates #132.

An additional change, is to name unnamed basic blocks (if not the
entry basic block). This change was introduced in LLVM 9.0 I think.

Essentially, for any block with a local ID that is not the entry block,
we use an explicit label (e.g. `2:`) instead of just adding a comment
(e.g. `; <label>:2`. This will require an update to the llir/llvm/ir
basic block output function.

asm/asm_test.go

@@ -90,6 +90,13 @@ func TestParseFile(t *testing.T) {
 		// parameter attribute.
 		{path: "../testdata/llvm/test/Transforms/InstSimplify/compare.ll"},
 
+		// Calling conventions.
+		{path: "../testdata/llvm/test/Bitcode/calling-conventions.3.2.ll"},
+		{path: "../testdata/llvm/test/CodeGen/X86/tailccfp.ll"},
+
+		// Parameter attributes (nofree).
+		{path: "../testdata/llvm/test/Transforms/Attributor/nonnull.ll"},
+
 		// Basic block labels.
 		{path: "../testdata/llvm/test/Assembler/block-labels.ll"},