[BOLT][Wrapper] Fix off-by-one when parsing 'cmp' output

[jobnoorman]

Summary

The byte offsets in the output of 'cmp' start from 1, not from 0 as the
current parser assumes. This caused mismatched bytes to sometimes be
attributed to the wrong section.

bolt/utils/llvm-bolt-wrapper.py

def compare_with(lhs, rhs, cmd, skip_begin=0, skip_end=0):
     cmp = compare_logs(run_lhs, run_rhs, skip_begin, skip_end)
     return cmp, run_lhs
 
 def parse_cmp_offset(cmp_out):
     '''
     Extracts byte number from cmp output:
     file1 file2 differ: byte X, line Y
     '''
-    return int(re.search(r'byte (\d+),', cmp_out).groups()[0])
+    # NOTE: cmp counts bytes starting from 1!
+    return int(re.search(r'byte (\d+),', cmp_out).groups()[0]) - 1
 
 def report_real_time(binary, main_err, cmp_err, cfg):
     '''
     Extracts real time from stderr and appends it to TIMING FILE it as csv:
     "output binary; base bolt; cmp bolt"
     '''
     def get_real_from_stderr(logline):
         return '; '.join(logline.split())