[x86] Changes and Additions to fix broken x86 build

Add missing syscalls to android/libc/arch-x86/syscalls

Remove #undef HAVE_GETLINE from platform.h
Fixes definition conflict warnings for x86 but is also
suitable for arm as  bionic has had a getline implementation for a
while now

Remove hardcoded CONFIG_CROSS_COMPILER_PREFIX from .config-full
and .config-minimal. This is now appended to  .config as part of
the prepare target in Android.mk

It appears no other changes are needed to other files such as
bbconfigopts.h etc as these are autogenerated when make prepare
is run.

Android.mk:
Added missing syscalls source to BUSYBOX_SRC_FILES when
TARGET_ARCH=x86.
Added appending of the CONFIG_CROSS_COMPILER_PREFIX to the .config
file based on the TARGET_ARCH

Change-Id: I4f550757b3209b852cd5a017e88dce50678e5734
android: add a script to regenerate prebuilt config

since x86 CROSS_COMPILER removal, it can be hard to do that properly

Change-Id: I6011e3b4dac5b5e670385df4812baf32f2e5ebc5
update config for 1.22.0

Change-Id: I38c5c30562a07e6ac0e7c58ad34b9b6ad99eceea
build: ignore selibs pkgconfig on android builds

This cause errors and is not required

Change-Id: If6cc6fb1595e83fac452d8a28cb4b8d250dff06d
Fix building on 4.4

Change-Id: I85030de3dea5f2d1a187cf2ced9517b3c820266a