Clean up forking and cloning.

The kernel now maintains the pthread_internal_t::tid field for us,
and __clone was only used in one place so let's inline it so we don't
have to leave such a dangerous function lying around. Also rename
files to match their content and remove some useless #includes.

Change-Id: I24299fb4a940e394de75f864ee36fdabbd9438f9

libc/arch-arm/arm.mk

@@ -1,7 +1,7 @@
 _LIBC_ARCH_COMMON_SRC_FILES := \
     arch-arm/bionic/abort_arm.S \
     arch-arm/bionic/atomics_arm.c \
-    arch-arm/bionic/clone.S \
+    arch-arm/bionic/__bionic_clone.S \
     arch-arm/bionic/eabi.c \
     arch-arm/bionic/_exit_with_stack_teardown.S \
     arch-arm/bionic/futex_arm.S \