Never pick up strawberry perl's pkg-config as a valid pkg-config

[nirbheek]

Strawberry Perl places a pkg-config.bat into PATH that is written in Perl and is not intended to be used by third parties as a MinGW distribution. This wouldn't matter, except that Strawberry Perl is also included in Github CI images out of the box, in PATH, and it breaks everyone's CI jobs.

This is already done by Meson and CMake.

Just filing this as an issue so I can link to it from rust-lang/rust#123436 for now, will open a PR to fix this later.

[nirbheek]

This is apparently not an issue due to pre-existing bugs in std::process::Command: rust-lang/rust#37519