Split asm and c flags and srcs in bp2build output

This allows removal of almost all current items from the mixed build
denylist, which were previously broken due to being unable to separately
control flags for compilations of different languages within the same
target.

Note that this does not appropriately implement asm/c srcs and flags for
either the shared variant or the static variant. This will require a
followup.

Test: bp2build.sh and mixed_libc.sh CI scripts
Test: Updated b2build tests

Change-Id: I28cf7437ee96cdf2fdbcb1eda2303691cff08ba4
diff --git a/cc/object.go b/cc/object.go
index 704cb69..cd71161 100644
--- a/cc/object.go
+++ b/cc/object.go
@@ -185,8 +185,14 @@
 	}
 	// TODO(b/183595872) warn/error if we're not handling product variables
 
+	// Don't split cc_object srcs across languages. Doing so would add complexity,
+	// and this isn't typically done for cc_object.
+	srcs := compilerAttrs.srcs
+	srcs.Append(compilerAttrs.cSrcs)
+	srcs.Append(compilerAttrs.asSrcs)
+
 	attrs := &bazelObjectAttributes{
-		Srcs:    compilerAttrs.srcs,
+		Srcs:    srcs,
 		Deps:    deps,
 		Copts:   compilerAttrs.copts,
 		Asflags: asFlags,