build_requires will be resolved too late to be of any help. build_requires are resolved by *after* Makefile.PL has already been executed by cpan/cpanp/cpanm etc.

CONFIGURE_REQUIRES on the other hand are a list of prereqs that must be resolved *before* Makefile.PL is executed.

• CONFIGURE_REQUIRES - modules required by Makefile.PL/Build.PL
• BUILD_REQUIRES - modules required only during the build process
• PREREQ_PM - modules required to run your module

WriteMakefile(
   CONFIGURE_REQUIRES => {
          'B' => 0,
   },
   PREREQ_PM => {
          'B' => 0,
   },
)
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We require the 'B' module during configuration and at runtime in the above example.