Implement armv6 optimized strlen from glibc 2.18

Change-Id: Ief985c9ca08cb74d9d7e41d3a583e62699f745cf
Add strcat_check/strcpy_check

Change-Id: I107a2b3374a7ea112c806f5cf0ea038abbdb5501
arm11.mk: include generic
bionic: improve tls/atomic support for armv6

bionic_atomic_arm.h:
 * include __ATOMIC_SWITCH_TO_THUMB and __ATOMIC_SWITCH_TO_ARM
   macros
 * add thumb-1 support, fix missing "+1" to enter THUMB mode
   in __ATOMIC_SWITCH_TO_THUMB

bionic_tls.h:
 * include __ATOMIC_SWITCH_TO_THUMB and __ATOMIC_SWITCH_TO_ARM
   macros
 * add thumb-1 support, fix missing "+1" to enter THUMB mode
   in __ATOMIC_SWITCH_TO_THUMB