ci: add useful c++ warning flags

[mzuzek]

Add -Wlogical-op-parentheses to CI build options.

Other commonly used flags for consideration:

• -Werror (warnings as errors - any breaks build)
• groups: -Wall, -Wextra, -pedantic
• unused: -Wunused, -Wunused-parameter, -Wunused-function, -Wunused-private-field
• -Wuninitialized
• -Wshadow
• -Wsign-compare
• -Wtype-limits
• -Wignored-qualifiers
• -Wempty-body

See more at https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html

[fnrizzi]

@cwschilly let's make a plan to decide what to add of these