Or other language flags that use CPPFLAGS (like CXXFLAGS). The problem
here is actually rather simple, `dict.setdefault()` doesn't work like I
thought it did, I thought it created a weak entry, but it actually is
equivalent to:
```python
if k not in dict:
dict[k] = v
```
Instead we'll use an intermediate dictionary (a default dictionary
actually, since that makes things a little cleaner) and then add the
keys from that dict to self.options as applicable.
Test case written by Jussi, Fix by Dylan
Co-authored-by: Jussi Pakkanen
Fixes: #8361Fixes: #8345
Currently mesonlib does some import tricks to figure out whether it
needs to use windows or posix specific functions. This is a little
hacky, but works fine. However, the way the typing stubs are implemented
for the msvcrt and fnctl modules will cause mypy to fail on the other
platform, since the functions are not implemented.
To aleviate this (and for slightly cleaner design), I've split mesonlib
into a pacakge with three modules. A universal module contains all of
the platform agnositc code, a win32 module contains window specific
code, a posix module contains the posix specific code, and a platform
module contains no-op implementations. Then the package's __init__ file
imports all of the universal functions and all of the functions from the
approriate platform module, or the no-op versions as fallbacks. This
makes mypy happy, and avoids `if`ing all over the code to switch between
the platform specific code.
Jussi Pakkanen