bionic: rename aarch64 target to arm64

Rename aarch64 build targets to arm64.  The gcc toolchain is still
aarch64.

Change-Id: Ia92d8a50824e5329cf00fd6f4f92eae112b7f3a3
diff --git a/linker/dlfcn.cpp b/linker/dlfcn.cpp
index 8501ad6..1e9d9bc 100644
--- a/linker/dlfcn.cpp
+++ b/linker/dlfcn.cpp
@@ -184,7 +184,7 @@
 #  define ANDROID_LIBDL_STRTAB \
     "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0android_get_LD_LIBRARY_PATH\0dl_iterate_phdr\0"
 #else
-#  error Unsupported architecture. Only aarch64, arm, mips, x86, and x86_64 are presently supported.
+#  error Unsupported architecture. Only arm, arm64, mips, x86, and x86_64 are presently supported.
 #endif
 
 static Elf_Sym gLibDlSymtab[] = {