Fix a compile error when HAGL_HAL_DEBUG is not defined

[SebKuzminsky]

Before this commit, if the user did not define HAGL_HAL_DEBUG the project would fail to compile because hagl_hal_debug() was syntactically incorrect.

This commit fixes the error by providing a valid hagl_hal_debug() function both when HAGL_HAL_DEBUG is defined and not. When HAGL_HAL_DEBUG is defined it prints the debug message, just like now. When HAGL_HAL_DEBUG is not defined, the function does not do anything.

[tuupola]

Better way to fix this is to define HAGL_HAL_DEBUG if it is not defined. Ie. something like:

#ifndef HAGL_HAL_DEBUG
#define HAGL_HAL_DEBUG         (0)
#endif

[SebKuzminsky]

Defining HAGL_HAL_DEBUG if it is not defined (as you suggested above) would work, but it's debatable whether that would be better. The solution proposed in this PR has the advantage that the compiler will optimize it out - there won't be any storage or runtime impact of hagl_hal_debug() statements.

But that said, i'd he happy to rework this PR to use your proposal if you prefer.

[tuupola]

Most compilers are smart enough to optimize out if (0) { ... }. See for example:

https://godbolt.org/z/qv77snYG4

[SebKuzminsky]

I switched this branch to use your suggestion.