Link libc++demangle with libc++ for the device.

libc++demangle provides __cxa_demangle, which used to be a part of
libc++.so but is being moved out to save on resources since very few
libraries need it.

Test: make checkbuild
Bug: http://b/138245375
Change-Id: Ie97225d496d7d40f8749522bf36702a2d9dcdfe7

cc/cc_test.go

@@ -1941,13 +1941,13 @@ func TestStaticLibDepExport(t *testing.T) {
 	// Check the shared version of lib2.
 	variant := "android_arm64_armv8-a_core_shared"
 	module := ctx.ModuleForTests("lib2", variant).Module().(*Module)
-	checkStaticLibs(t, []string{"lib1", "libclang_rt.builtins-aarch64-android", "libatomic", "libgcc_stripped"}, module)
+	checkStaticLibs(t, []string{"lib1", "libc++demangle", "libclang_rt.builtins-aarch64-android", "libatomic", "libgcc_stripped"}, module)
 
 	// Check the static version of lib2.
 	variant = "android_arm64_armv8-a_core_static"
 	module = ctx.ModuleForTests("lib2", variant).Module().(*Module)
 	// libc++_static is linked additionally.
-	checkStaticLibs(t, []string{"lib1", "libc++_static", "libclang_rt.builtins-aarch64-android", "libatomic", "libgcc_stripped"}, module)
+	checkStaticLibs(t, []string{"lib1", "libc++_static", "libc++demangle", "libclang_rt.builtins-aarch64-android", "libatomic", "libgcc_stripped"}, module)
 }
 
 var compilerFlagsTestCases = []struct {

cc/stl.go

@@ -161,6 +161,15 @@ func (stl *stl) deps(ctx BaseModuleContext, deps Deps) Deps {
 		} else {
 			deps.StaticLibs = append(deps.StaticLibs, stl.Properties.SelectedStl)
 		}
+		if ctx.Device() && !ctx.useSdk() {
+			// __cxa_demangle is not a part of libc++.so on the device since
+			// it's large and most processes don't need it. Statically link
+			// libc++demangle into every process so that users still have it if
+			// needed, but the linker won't include this unless it is actually
+			// called.
+			// http://b/138245375
+			deps.StaticLibs = append(deps.StaticLibs, "libc++demangle")
+		}
 		if ctx.toolchain().Bionic() {
 			if ctx.Arch().ArchType == android.Arm {
 				deps.StaticLibs = append(deps.StaticLibs, "libunwind_llvm")

cc/testing.go

@@ -166,6 +166,16 @@ func GatherRequiredDepsForTest(os android.OsType) string {
 				support_system_process: true,
 			},
 		}
+		cc_library {
+			name: "libc++demangle",
+			no_libcrt: true,
+			nocrt: true,
+			system_shared_libs: [],
+			stl: "none",
+			host_supported: false,
+			vendor_available: true,
+			recovery_available: true,
+		}
 		cc_library {
 			name: "libunwind_llvm",
 			no_libcrt: true,