build: fix unknown warning option

warning: unknown warning option '-Wno-int-in-bool-context'; did you mean '-Wno-gnu-include-next'? [-Wunknown-warning-option] 1 warning generated.

The -Wint-in-bool-context diagnostic is not enabled by default, so no additional option is needed.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines