Improve env interpolate error message.
Improve env lookup failures to print all values as well.
MSVC project fixes

- Only overwrite .vcxproj files on changes.
- Don't try to built meta projects.
MOAR! MSVC project fixes

- In multiple solutions, only build the projects specified in the hints.
- Also add INCLUDE-specified directories to the NMake intellisense hints, so MSVC can figure out that types defined in e.g. stdint.h are in fact types.