[BOLT][TEST] Use double dash flags in tests

[BOLT][TEST] Use double dash flags in tests

Replace a single dash with a double dash for options that have more
than a single letter.

llvm-bolt-wrapper.py has special treatment for output options such as
"-o" and "-w" causing issues when a single dash is used, e.g. for
"-write-dwp". The wrapper can be fixed as well, but using a double dash
has other advantages as well.

Reviewed By: rafauler

Differential Revision: https://reviews.llvm.org/D127538