remove LogMessage prototype from plc_main_head.c

it's not needed, because prototype is included in beremiz.h
But it caused problems with TARGET_LOGGING_DISABLE.

merge

Make online debug optional

It could be useful for very small targets like Atmega (Arduino) and
for target bring-up there developer want to have running PLC program,
but has not implemented runtime communication yet.


TARGET_DEBUG_AND_RETAIN_DISABLE - completely disable debug and retain
functionality. Previously named TARGET_DEBUG_DISABLE.

TARGET_ONLINE_DEBUG_DISABLE - can be used to enable retain
functionality (no define TARGET_DEBUG_AND_RETAIN_DISABLE is used), but disable
online debug with corresponding RAM/FLASH overhead.

TARGET_LOGGING_DISABLE - disables logging functionality from runtime and PLC program

TARGET_EXT_SYNC_DISABLE - disables PLC program synchronization with
external events. For example, it could be used to synchronize several
PLCs that control motors for different axes.

By default all these options are off.

To test generate program for Generic target, put following files in
project files directory and run build.sh after generating PLC program.
This is very easy to integrate into makefile (Generic target).

[------------- build.sh --------------------------]
files=$(find $PWD/../build -iname '*.c' | grep -v POUS.c)
arm-none-eabi-gcc \
-DTARGET_DEBUG_AND_RETAIN_DISABLE \
-DTARGET_ONLINE_DEBUG_DISABLE \
-DTARGET_LOGGING_DISABLE \
-DTARGET_EXT_SYNC_DISABLE \
-flto -ffunction-sections -fdata-sections -I../../../../matiec/lib/C \
$files \
main.c \
-Wl,--Map=./program.map,--cref \
-nodefaultlibs --specs=nano.specs -Wl,--static -Wl,--gc-section -Wl,--start-group -lc -lm -lnosys -lgcc -Wl,--end-group
[------------------------------------------------]

[------------- main.c --------------------------]
#ifndef TARGET_DEBUG_AND_RETAIN_DISABLE
void Retain(void){}
void InValidateRetainBuffer(void){}
void ValidateRetainBuffer(void){}
#endif

extern void __run(void);
int main(void)
{
for(;;) {
__run();
// sleep common_ticktime__ ns
// add common_ticktime__ ns to __CURRENT_TIME
}
return 0;
}
[------------------------------------------------]

Disable Python extension in First steps example