GCC fails to build libasan with -mthumb and -fno-omit-frame-pointer

GCC fails to build libasan with -mthumb and -fno-omit-frame-pointer

GCC does not allow to have frame pointer register as a clobber register
for inline assembler, when flag -fno-omit-frame-pointer is added.
By default, arm with mthumb mode uses r7 as a frame pointer register.

https://reviews.llvm.org/D50180

Backport:
  https://review.tizen.org/gerrit/gitweb?p=platform/upstream/linaro-gcc.git
  commit: 0de5898b

Change-Id: I5f5a3c695353ba2fe4195fd6054aedb7ee11e1af
Signed-off-by: Vyacheslav Cherkashin <v.cherkashin@samsung.com>