Fix build by avoiding the _C_LABEL macro.

Change-Id: Ide367c2b65071388bd95fbc81a4ed6ae94aec4e4
diff --git a/libc/arch-x86_64/syscalls/truncate.S b/libc/arch-x86_64/syscalls/truncate.S
index 5e5eb8e..dfb6687 100644
--- a/libc/arch-x86_64/syscalls/truncate.S
+++ b/libc/arch-x86_64/syscalls/truncate.S
@@ -15,5 +15,5 @@
     ret
 END(truncate)
 
-    .globl _C_LABEL(truncate64)
-    .equ _C_LABEL(truncate64), _C_LABEL(truncate)
+    .globl truncate64
+    .equ truncate64, truncate