Clean up uses of the bool type and make them consistent

[bryanpkc]

Some general observation regarding the use of the bool type. Some of the files try to do 'the right thing', by adding inclusion of the stdbool.h header and even handle the lack of it on Windows. All-lower-case bool, true, false is used there. Other places inherit the initial flang mess with bool type used lowercase with TRUE and FALSE uppercase literals.

Originally posted by @pawosm-arm in #1215 (comment)