There are some testcase failures when -fstack-protector is turned on
during testcase compilation, reported here,

  https://bugs.launchpad.net/gdb-linaro/+bug/616000

This bug is found on both arm and i386, but has to be fixed respectively.

This patch is to address this problem by matching insn pattern (movw,
movt, ldr, and str), and expand post_prologue_pc to skip insns for stack
protector.  Existing {arm,thumb}_analyze_prologue has capability to skip
these insns, so they are not changed.

Regression tested with combination of
"\{-mthumb,-marm\}\{-fstack-protector,-fno-stack-protector}\{-march=armv7-a,-march=armv5t\}".
 OK for mainline?

-- 
Yao (齐尧)