Remove the useless _C_LABEL from generated system calls.

Change-Id: Id1d2fd39972652831ea825f6f9cf940b08f42b5c
diff --git a/libc/arch-mips64/syscalls/__brk.S b/libc/arch-mips64/syscalls/__brk.S
index c352c69..99a108a 100644
--- a/libc/arch-mips64/syscalls/__brk.S
+++ b/libc/arch-mips64/syscalls/__brk.S
@@ -23,4 +23,4 @@
     move ra, t0
     .set pop
 END(__brk)
-.hidden _C_LABEL(__brk)
+.hidden __brk