[ARM] Rework expectation for call to Armv8-M nonsecure function

[ARM] Rework expectation for call to Armv8-M nonsecure function

Testcase gcc.target/arm/cmse/cmse-14.c checks whether bar is called via
__gnu_cmse_nonsecure_call libcall and not via a direct call. However the
pattern is a bit surprising in that it needs to explicitely allow "by"
due to allowing anything before the 'b'.

This patch rewrites the logic to look for b as a first non-whitespace
letter followed iby anything (to match bl and conditional branches)
followed by some spaces and then bar.

2017-11-17  Thomas Preud'homme  <thomas.preudhomme@arm.com>

    gcc/testsuite/
    * gcc.target/arm/cmse/cmse-14.c: Change logic to match branch
    instruction to bar.

From-SVN: r254861