nptl: compile pt-vfork in ARM-mode

could need a thumb implementation..

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

libpthread/nptl/sysdeps/unix/sysv/linux/arm/Makefile.arch

@@ -17,4 +17,4 @@ libc_linux_arch_SSRC-OMIT = waitpid.S
 # We always compile it in arm mode because of SAVE_PID macro
 # This macro should be alternatively implemented in THUMB
 # assembly.
-ASFLAGS-vfork.S = -marm
+ASFLAGS-pt-vfork.S = -marm