shared/bpm: Replace sprintf usage

[jcm93]

Description

Replace sprintf use in bpm with safer snprintf, providing the length of the remaining buffer space in the string as the size parameter to snprintf.

Motivation and Context

sprintf use can fire -Wdeprecated in AppleClang, causing build failures under typical -Werror OBS compilation settings.

For some reason, locally, this use of sprintf only seems to fire -Wdeprecated when the address sanitizer is on, even though it seems like we ought to be hitting it in all circumstances. Regardless, we want to be able to compile with ASAN, and sprintf use is typically unsafe, so replace with a safer alternative.

How Has This Been Tested?

Enabled BPM, made sure it is still writing correct timestamps.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

• Code cleanup (non-breaking change which makes code smaller or more readable)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[jcm93]

The first version of this PR tried to be smart and assumed that "%03ld" would be no more than 3 characters in length, because it was formatting a timespec nanosecond value that had been divided by one million. This was not good enough of a guarantee for GCC, which complained that for longer long values, 3 bytes would not be enough.

The current version of the code just provides the entirety of the string's remaining buffer space as the size parameter to snprintf.