Revert r299923, it doesn't build in bootstrap builds.

FAILED: lib/sanitizer_common/CMakeFiles/RTSanitizerCommon.arm.dir/sanitizer_linux.cc.o 
lib/sanitizer_common/sanitizer_linux.cc:1340:24: error: invalid instruction
                       BLX(ip)
                       ^
lib/sanitizer_common/sanitizer_linux.cc:1313:19: note: expanded from macro 'BLX'
#  define BLX(R) "mov lr, pc; bx" #R "\n"
                  ^
<inline asm>:6:13: note: instantiated into assembly here
mov lr, pc; bxip
            ^~~~

llvm-svn: 299943