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
diff --git a/libc/arch-x86/x86.mk b/libc/arch-x86/x86.mk
index 5911ad9..9c74084 100644
--- a/libc/arch-x86/x86.mk
+++ b/libc/arch-x86/x86.mk
@@ -1,5 +1,5 @@
 _LIBC_ARCH_COMMON_SRC_FILES := \
-    arch-x86/bionic/clone.S \
+    arch-x86/bionic/__bionic_clone.S \
     arch-x86/bionic/_exit_with_stack_teardown.S \
     arch-x86/bionic/futex_x86.S \
     arch-x86/bionic/__get_sp.S \