build: Fix python path resolution in configure

[digitalinfinity]

The check to validate whether the current python process is the same as
the one resolved from the current path fails if the paths differ by case
which can happen on an operating system with case insensitive file
system behavior like Windows. Canonicalize it by converting both to
lower case if running on Windows.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

Affected core subsystem(s)

build