Fix build by avoiding the _C_LABEL macro.

Change-Id: Ide367c2b65071388bd95fbc81a4ed6ae94aec4e4
diff --git a/libc/arch-x86_64/syscalls/prlimit64.S b/libc/arch-x86_64/syscalls/prlimit64.S
index b451e8f..12be53a 100644
--- a/libc/arch-x86_64/syscalls/prlimit64.S
+++ b/libc/arch-x86_64/syscalls/prlimit64.S
@@ -16,5 +16,5 @@
     ret
 END(prlimit64)
 
-    .globl _C_LABEL(prlimit)
-    .equ _C_LABEL(prlimit), _C_LABEL(prlimit64)
+    .globl prlimit
+    .equ prlimit, prlimit64