adding support for pthread_mutex_lock handling

[sona78]

Updates:

• Standardized pthread_mutex_lock handling with replacement with interruptible locks for error handling
• Updated proc_loadavg.c with more robust handling to unlock mutexes that will cause errors

[mihalicyn]

a few things to consider:

• this code does not compile
• there is not Signed-off-by tag in the commit message
• please, explain a reason for this change