Don't use build CFLAGS and friends as target settings
Don't use build CFLAGS and friends as target settings
In the GHC in tree configure, `CFLAGS`, `CXXFLAGS`, and similar tool
configuration flags apply to the BUILD phase of the compiler, i.e. to
the tools run to compile GHC itself.
Notably, they should /not/ be carried over to the Target settings, i.e.
these flags should /not/ apply to the tool which GHC invokes at runtime.
Fixes #25637 (closed)