Specify the API level via the triple instead of __ANDROID_API__.

Clang derives the value of __ANDROID_API__ from the triple these days. In a
future version of clang I plan to start making the behaviour of the HWASAN pass
dependent on the API level in the triple, so it's going to need to be accurate.

Test: walleye-userdebug boots
Change-Id: Ie5e36b5c8f6dcda084cc12b1160abbdf94765174
diff --git a/cc/makevars.go b/cc/makevars.go
index 2b49772..acac455 100644
--- a/cc/makevars.go
+++ b/cc/makevars.go
@@ -249,9 +249,9 @@
 	}
 
 	clangPrefix := secondPrefix + "CLANG_" + typePrefix
-	clangExtras := "-target " + toolchain.ClangTriple()
-	clangExtras += " -B" + config.ToolPath(toolchain)
+	clangExtras := "-B" + config.ToolPath(toolchain)
 
+	ctx.Strict(clangPrefix+"TRIPLE", toolchain.ClangTriple())
 	ctx.Strict(clangPrefix+"GLOBAL_CFLAGS", strings.Join([]string{
 		toolchain.ClangCflags(),
 		"${config.CommonClangGlobalCflags}",