Implement notion of a "container format" (#213)

The big addition here is that the Slang "bytecode" is no longer treated as just a "code generation target" (`CodeGenTarget`) akin to DX bytecode (DXBC) or SPIR-V, but instead is a `ContainerFormat` that can be used to emit all the results of a compile request (well, currently just the IR-as-BC, but the intention is there).

Getting to this goal involved some prior checkins that eliminated bogus "targets" that weren't really akin to SPIR-V or DXBC: `-target slang-ir-asm` and `-target reflection-json`. Those targets were really in place to support testing, and so they've been made more explicit testing/debug options.

This change eliminates `-target slang-ir` and instead tries to allow the user to specify `-o foo.slang-module` as an output file name, that indicates the intention to output a "container" file that will wrap up all the generated code.

I've also gone ahead and generalized the existing `-target` option so that we are actually building up a *list* of code generation targets. This is largely just a cleanup, since it forces code to be more aware of when it is doing something target-specific vs. target independent. For example, reflection layout information lives on a requested target, and not on the compile request as a whole, and similarly output code is per-target, per-entry-point.

As a cleanup, I eliminated support for per-translation-unit output. This was vestigial code from back when I used to try and do HLSL generation for a whole translation unit instead of per-entry-point (which turned out to be a lot of complexity for little gain), and it was only being used in the `hello` example and the `render-test` test fixture - in both cases fixing it up was easy enough. I've stubbed out the old `spGetTranslationUnitSource` API, but haven't removed it yet.

1 files changed, 19 insertions, 3 deletions

diff --git a/source/slang/bytecode.h b/source/slang/bytecode.h
index 1ea16406f..f38007ba9 100644
--- a/source/slang/bytecode.h
+++ b/source/slang/bytecode.h
@@ -225,11 +225,27 @@ struct BCHeader
     // kinds of data without having to revise
     // the schema here.
 
-    // The bytecode representation of the module
-    BCPtr<BCModule>     module;
+    // TODO: should include AST declaration structure
+    // here, which can be used for refleciton, and
+    // also loaded to resolve dependencies when
+    // compiling other modules.
+
+    // TODO: Include the original entry point requests?
+
+    // Zero or more IR modules, corresponding to
+    // the translation units of the original compile
+    // request.
+    uint32_t                moduleCount;
+    BCPtr<BCPtr<BCModule>>  modules;
+
+    // TODO: should enumerate targets here, and
+    // include reflection layout info + compiled
+    // entry points for each target.
 };
 
-
+struct CompileRequest;
+void generateBytecodeForCompileRequest(
+    CompileRequest* compileReq);
 
 }