Nimsuggest (in VS Code) raises assertionErrors on Windows when copying using cmd
## Code to reproduce
```nim
import nimterop/[build, cimport]
#static:
#    cDebug()
#    cDisableCaching()

const baseDir = getProjectCacheDir("symengine")

setDefines(@["cwrapperJBB", "cwrapperSetVer=0.6.0"])

getHeader( # HERE!
    "cwrapper.h",
    jbbUri = "symengine",
    outdir = baseDir,
    altNames = "symengine"
    )

cIncludeDir(baseDir / "symengine/include")
cIncludeDir(baseDir / "GMP/include")
cIncludeDir(baseDir / "MPFR/include")
cIncludeDir(baseDir / "MPC/include")

static:
  discard gorgeEx("ln -sf libsymengine.so libsymengine.so.0.6")
  cSkipSymbol(@[
    "basic_get_type", "basic_get_class_id", "basic_get_class_from_id"])

cPassL(cwrapperLPath)
import strutils
cPassL(join(cwrapperLDeps, " "))
cPassL("-Wl,-rpath -Wl,.")
cImport(cwrapperPath, recurse = true,flags = "--prefix:__,_ --suffix:__,_")
```

## Observed behavior
At the call of `getHeader` marked with "HERE!" Nimsuggest gives 9 errors like this one:
```
template/generic instantiation of `getHeader` from here

cmd /c copy /y C:\Users\hugog\nimcache\nimterop\symengine\GMP\bin\libgmp-10.dll c:\Users\hugog\code\nim\symengine.nim\src\symengine\libgmp-10.dll [AssertionError]
stack trace: (most recent call last)
C:\Users\hugog\.nimble\pkgs\nimterop-0.6.8\nimterop\build\getheader.nim(536, 25)
```
The src file exists but the destination file doesn't get copied.
## Expected behavior
It shouldn't raise those errors😝

## Notes
I can't reproduce this on Linux so it seems like it is Windows specific
 