FindPkgConfig: Backslashes in pkg-config output on Windows

When getting a string from pkg-config in FindPkgConfig.cmake, which contains a path from backslashes (windows). It normalizes this with: -LC:\gtk-build\gtk\x64\release/lib → C:gtk-buildgtkx64release/lib This also happens later on path normalization. Therefore, the PkgConfig produces broken targets on Windows.

Tested it with: FindPkgConfig.cmake(137,1):

  if (_pkgconfig_failed)
    set(_pkgconfig_${_varname} "")
    _pkgconfig_unset(${_prefix}_${_varname})
  else()
 +    if (WIN32)
 +      string(REGEX REPLACE "\\" "/" _pkgconfig_invoke_result "${_pkgconfig_invoke_result}")
 +    endif()
 +    message(STATUS "_pkgconfig_invoke_result: ${_pkgconfig_invoke_result}")
    string(REGEX REPLACE "[\r\n]"       " " _pkgconfig_invoke_result "${_pkgconfig_invoke_result}")

Note that this works as expected:

      string(REPLACE "\\" "/" _pkgconfig_invoke_result "${_pkgconfig_invoke_result}")