Use "${config.ClangBin}/llvm-" for TOOLS_PREFIX.

We're removing GNU binutils in Android T, so lets redirect any last
remaining users to the LLVM equivalents sooner rather than later.

(This won't "just work" for ld versus lld, but it's likely that anyone
using TOOLS_PREFIX will need a few other tweaks anyway, and including
the "llvm-" prefix seems like it will cover most other cases.)

Bug: http://b/185257607
Test: treehugger
Change-Id: Ibb5efbbef801419e7d8258d6d8b67572df66e7d0
diff --git a/cc/makevars.go b/cc/makevars.go
index da5f1fd..2b326ef 100644
--- a/cc/makevars.go
+++ b/cc/makevars.go
@@ -288,9 +288,7 @@
 		ctx.Strict(makePrefix+"OBJCOPY", "${config.ClangBin}/llvm-objcopy")
 		ctx.Strict(makePrefix+"LD", "${config.ClangBin}/lld")
 		ctx.Strict(makePrefix+"NDK_TRIPLE", config.NDKTriple(toolchain))
-		// TODO: work out whether to make this "${config.ClangBin}/llvm-", which
-		// should mostly work, or remove it.
-		ctx.Strict(makePrefix+"TOOLS_PREFIX", gccCmd(toolchain, ""))
+		ctx.Strict(makePrefix+"TOOLS_PREFIX", "${config.ClangBin}/llvm-")
 		// TODO: GCC version is obsolete now that GCC has been removed.
 		ctx.Strict(makePrefix+"GCC_VERSION", toolchain.GccVersion())
 	}