Fix clang-tidy return value reporting (Part Ⅱ)
Fix clang-tidy return value reporting (Part Ⅱ)

It turns out my first attempt to fix this in 00d5ef3191e5 ("Fix
clang-tidy return value reporting (#7949)") is not sufficient: The
local variable returncode is never updated and stays at 0. This fixes
the returncode calculation.

Fixes: cce172432be3 ("Use run-clang-tidy when available.")

mesonbuild/meson,mesonbuild/meson,QuLogic/meson,pexip/meson,jpakkane/meson,QuLogic/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,jpakkane/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,QuLogic/meson,jpakkane/meson,QuLogic/meson,jpakkane/meson,QuLogic/meson,jpakkane/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,QuLogic/meson,pexip/meson,pexip/meson,mesonbuild/meson,jpakkane/meson,QuLogic/meson,jpakkane/meson,pexip/meson,QuLogic/meson,pexip/meson,jpakkane/meson,jpakkane/meson,pexip/meson,pexip/meson,QuLogic/meson