Prettify soong ninja build descriptions

Descriptions currently look like:
[  0% 4/29328] cc out-soong/.intermediates/external/clang/lib/Sema/libclangSema/android_arm_armv7-a-neon_denver_static_core/obj/external/clang/lib/Sema/SemaCodeComplete.o

This is not very helpful - most of the characters are used to show the
output path, which contains useful information like target architecture,
but also contains most of the path to the source files twice, and less
useful information like the exact variant name used by soong.
Make the descriptions look like:
[  0% 3/29329] //external/clang/lib/Sema:libclangSema clang++ SemaTemplateInstantiate.cpp

This is //path/to/module:modulename tool relative/path/to/source/file

Test: builds, looks pretty
Change-Id: I3087aa7d4eb1860ef6239d77407b8b35445616d7

1 files changed, 1 insertions, 1 deletions

diff --git a/cc/rs.go b/cc/rs.go
index a001f89e..976107ea 100644
--- a/cc/rs.go
+++ b/cc/rs.go
@@ -39,7 +39,6 @@ var (
 			CommandDeps: []string{"$rsCmd"},
 			Depfile:     "${out}.d",
 			Deps:        blueprint.DepsGCC,
-			Description: "rsCpp $out",
 		},
 		"depFiles", "outDir", "rsFlags", "stampFile")
 )
@@ -67,6 +66,7 @@ func rsGenerateCpp(ctx android.ModuleContext, rsFiles android.Paths, rsFlags str
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
 		Rule:            rsCpp,
+		Description:     "llvm-rs-cc",
 		Output:          stampFile,
 		ImplicitOutputs: cppFiles,
 		Inputs:          rsFiles,