chromium: Ignore unknown warning options

This can e.g. save around 150k lines of unnecessary log messages which
take up around 66% of the total lines (based on a log of 80.0.3987.100):
29527 warning: unknown warning option '-Wno-bitwise-conditional-parentheses'; did you mean '-Wno-bitwise-op-parentheses'? [-Wunknown-warning-option]
29527 warning: unknown warning option '-Wno-builtin-assume-aligned-alignment' [-Wunknown-warning-option]
29527 warning: unknown warning option '-Wno-deprecated-copy'; did you mean '-Wno-deprecated'? [-Wunknown-warning-option]
29527 warning: unknown warning option '-Wno-final-dtor-non-final-class'; did you mean '-Wno-abstract-final-class'? [-Wunknown-warning-option]
29527 warning: unknown warning option '-Wno-implicit-int-float-conversion'; did you mean '-Wno-implicit-float-conversion'? [-Wunknown-warning-option]

pkgs/applications/networking/browsers/chromium/common.nix

···
       runHook postConfigure
     '';
 
+    # Don't spam warnings about unknown warning options. This is useful because
+    # our Clang is always older than Chromium's and the build logs have a size
+    # of approx. 25 MB without this option (and this saves e.g. 66 %).
+    NIX_CFLAGS_COMPILE = "-Wno-unknown-warning-option";
+
     buildPhase = let
       # Build paralelism: on Hydra the build was frequently running into memory
       # exhaustion, and even other users might be running into similar issues.