Cython can be used with more than one Python installation, and the
sanity check cannot know which one a project will use. A failure to
build the transpiled source against the default Python therefore does
not mean that the project will fail.
Split out the compiler invocation part of Compiler.sanity_check, so
that the Cython compiler can print a warning in that case and proceed
nevertheless. Failures to transpile, however, remain an error.
Fixes: #15740
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Paolo Bonzini
df369aa3fd