doxygen: Make it build with ninja 1.9.0
doxygen: Make it build with ninja 1.9.0

ninja 1.9.0 turned the previous dupbuild warning into an error, which
resulted in the following error:

  ninja: error: build.ninja:1948: multiple rules generate
  generated_src/configvalues.h [-w dupbuild=err]

Turn the error back into a warning until upstream corrects the build
rules.

Signed-off-by: Peter Kjellerstedt <acc79ae48f6d90868791bcb456f6177f58b04c14@axis.com>
Signed-off-by: Khem Raj <729d64b6f67515e258459a5f6d20ec88b2caf8df@gmail.com>

VCTLabs/meta-openembedded,victronenergy/meta-openembedded,VCTLabs/meta-openembedded,VCTLabs/meta-openembedded,moto-timo/meta-openembedded,openembedded/meta-openembedded,rehsack/meta-openembedded,openembedded/meta-openembedded,moto-timo/meta-openembedded,openembedded/meta-openembedded,moto-timo/meta-openembedded,schnitzeltony/meta-openembedded,openembedded/meta-openembedded,rehsack/meta-openembedded,VCTLabs/meta-openembedded,schnitzeltony/meta-openembedded,lgirdk/meta-openembedded,schnitzeltony/meta-openembedded,openembedded/meta-openembedded,openembedded/meta-openembedded,victronenergy/meta-openembedded,VCTLabs/meta-openembedded,victronenergy/meta-openembedded,rehsack/meta-openembedded,VCTLabs/meta-openembedded,mrchapp/meta-openembedded,rehsack/meta-openembedded,lgirdk/meta-openembedded,mrchapp/meta-openembedded,lgirdk/meta-openembedded,rehsack/meta-openembedded,lgirdk/meta-openembedded,mrchapp/meta-openembedded,schnitzeltony/meta-openembedded,openembedded/meta-openembedded,VCTLabs/meta-openembedded,lgirdk/meta-openembedded,victronenergy/meta-openembedded,mrchapp/meta-openembedded,victronenergy/meta-openembedded,lgirdk/meta-openembedded,mrchapp/meta-openembedded,rehsack/meta-openembedded,VCTLabs/meta-openembedded,openembedded/meta-openembedded,schnitzeltony/meta-openembedded,mrchapp/meta-openembedded,moto-timo/meta-openembedded,schnitzeltony/meta-openembedded,mrchapp/meta-openembedded,lgirdk/meta-openembedded,rehsack/meta-openembedded,moto-timo/meta-openembedded,schnitzeltony/meta-openembedded,victronenergy/meta-openembedded,victronenergy/meta-openembedded