Yet more msvc and windows fixes

commit 6031365b:

cerbero: Fix syntax errors in VS env functions
And also some logic errors.

commit 20cd6f76:

glib-tools.recipe: Fix build on Windows with MinGW

commit 43d7ee5b:

windows.config: Use MSVC rc instead of GNU windres
We were accidentally always using GNU windres, which meant no symbols
for the resources.

commit 291839b5:

cerbero/msvc: Better way to export the MSVC shell
Instead of exporting exactly once, check if the variable already has
the values we want to add, and don't add it if it does. This fixes
a potential issue where we set the some env var earlier and want to
append to it when exporting for MSVC, which would result in the var
not being set at all.

commit f7229044:

cerbero: Prefer lib.exe over dlltool to find DLLs
dlltool does not support all architectures of import libraries, f.ex.,
it does not work at all with ARMv7 and ARM64 binaries.

lib.exe should be preferred since it's also twice as fast as dlltool,
and it will be available if we're building for those archs.