Allow use of log_x() in if

[FrankBoesing]

if (1) log_e("error") produces a warning ("missing braces") and probably wrong code if no log level is defined.
This fixes that.

[CLAassistant]

All committers have signed the CLA.

[me-no-dev]

Nice solution :)

[marcboon]

I've seen this solution before, but why 'do {} while(0)' instead of just '{}' ?

[FrankBoesing]

Because this is a systax error:

#define foo {}

if (1) foo; 
else {}

This not:

#define foo do {} while(0)

if (1) foo; 
else {}